Merge Arel into Active Record

146 files changed, 11277 insertions, 4 deletions

diff --git a/.rubocop.yml b/.rubocop.yml
index 3c765d5b1d..aa998b8f26 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -7,6 +7,9 @@ AllCops:
     - '**/templates/**/*'
     - '**/vendor/**/*'
     - 'actionpack/lib/action_dispatch/journey/parser.rb'
+    - 'activerecord/lib/arel.rb'
+    - 'activerecord/lib/arel/**/*'
+    - 'activerecord/test/cases/arel/**/*'
 
 # Prefer &&/|| over and/or.
 Style/AndOr:
diff --git a/Gemfile.lock b/Gemfile.lock
index baac1cee7e..f3d5b52a4e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -57,7 +57,6 @@ PATH
     activerecord (6.0.0.alpha)
       activemodel (= 6.0.0.alpha)
       activesupport (= 6.0.0.alpha)
-      arel (>= 9.0)
     activestorage (6.0.0.alpha)
       actionpack (= 6.0.0.alpha)
       activerecord (= 6.0.0.alpha)
@@ -106,7 +105,6 @@ GEM
     amq-protocol (2.2.0)
     archive-zip (0.7.0)
       io-like (~> 0.3.0)
-    arel (9.0.0)
     ast (2.4.0)
     aws-partitions (1.20.0)
     aws-sdk-core (3.3.0)
diff --git a/activerecord/MIT-LICENSE b/activerecord/MIT-LICENSE
index cce00cbc3a..04ba107c48 100644
--- a/activerecord/MIT-LICENSE
+++ b/activerecord/MIT-LICENSE
@@ -1,5 +1,7 @@
 Copyright (c) 2004-2018 David Heinemeier Hansson
 
+Arel originally copyright (c) 2007-2016 Nick Kallen, Bryan Helmkamp, Emilio Tagua, Aaron Patterson
+
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
diff --git a/activerecord/activerecord.gemspec b/activerecord/activerecord.gemspec
index b43e7c50f5..a857d00c05 100644
--- a/activerecord/activerecord.gemspec
+++ b/activerecord/activerecord.gemspec
@@ -30,6 +30,4 @@ Gem::Specification.new do |s|
 
   s.add_dependency "activesupport", version
   s.add_dependency "activemodel",   version
-
-  s.add_dependency "arel", ">= 9.0"
 end
diff --git a/activerecord/lib/arel.rb b/activerecord/lib/arel.rb
new file mode 100644
index 0000000000..c327caeac0
--- /dev/null
+++ b/activerecord/lib/arel.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+require 'arel/errors'
+
+require 'arel/crud'
+require 'arel/factory_methods'
+
+require 'arel/expressions'
+require 'arel/predications'
+require 'arel/window_predications'
+require 'arel/math'
+require 'arel/alias_predication'
+require 'arel/order_predications'
+require 'arel/table'
+require 'arel/attributes'
+require 'arel/compatibility/wheres'
+
+require 'arel/visitors'
+require 'arel/collectors/sql_string'
+
+require 'arel/tree_manager'
+require 'arel/insert_manager'
+require 'arel/select_manager'
+require 'arel/update_manager'
+require 'arel/delete_manager'
+require 'arel/nodes'
+
+module Arel
+  VERSION = '10.0.0'
+
+  def self.sql raw_sql
+    Arel::Nodes::SqlLiteral.new raw_sql
+  end
+
+  def self.star
+    sql '*'
+  end
+  ## Convenience Alias
+  Node = Arel::Nodes::Node
+end
diff --git a/activerecord/lib/arel/alias_predication.rb b/activerecord/lib/arel/alias_predication.rb
new file mode 100644
index 0000000000..cb50fb95be
--- /dev/null
+++ b/activerecord/lib/arel/alias_predication.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+module Arel
+  module AliasPredication
+    def as other
+      Nodes::As.new self, Nodes::SqlLiteral.new(other)
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/arel/attributes.rb b/activerecord/lib/arel/attributes.rb
new file mode 100644
index 0000000000..ed4739ebed
--- /dev/null
+++ b/activerecord/lib/arel/attributes.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require 'arel/attributes/attribute'
+
+module Arel
+  module Attributes
+    ###
+    # Factory method to wrap a raw database +column+ to an Arel Attribute.
+    def self.for column
+      case column.type
+      when :string, :text, :binary             then String
+      when :integer                            then Integer
+      when :float                              then Float
+      when :decimal                            then Decimal
+      when :date, :datetime, :timestamp, :time then Time
+      when :boolean                            then Boolean
+      else
+        Undefined
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/attributes/attribute.rb b/activerecord/lib/arel/attributes/attribute.rb
new file mode 100644
index 0000000000..41bc0c32c7
--- /dev/null
+++ b/activerecord/lib/arel/attributes/attribute.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+module Arel
+  module Attributes
+    class Attribute < Struct.new :relation, :name
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+      include Arel::Math
+
+      ###
+      # Create a node for lowering this attribute
+      def lower
+        relation.lower self
+      end
+
+      def type_cast_for_database(value)
+        relation.type_cast_for_database(name, value)
+      end
+
+      def able_to_type_cast?
+        relation.able_to_type_cast?
+      end
+    end
+
+    class String    < Attribute; end
+    class Time      < Attribute; end
+    class Boolean   < Attribute; end
+    class Decimal   < Attribute; end
+    class Float     < Attribute; end
+    class Integer   < Attribute; end
+    class Undefined < Attribute; end
+  end
+
+  Attribute = Attributes::Attribute
+end
diff --git a/activerecord/lib/arel/collectors/bind.rb b/activerecord/lib/arel/collectors/bind.rb
new file mode 100644
index 0000000000..d816aed90d
--- /dev/null
+++ b/activerecord/lib/arel/collectors/bind.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module Arel
+  module Collectors
+    class Bind
+      def initialize
+        @binds = []
+      end
+
+      def << str
+        self
+      end
+
+      def add_bind bind
+        @binds << bind
+        self
+      end
+
+      def value
+        @binds
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/composite.rb b/activerecord/lib/arel/collectors/composite.rb
new file mode 100644
index 0000000000..4f6156fe27
--- /dev/null
+++ b/activerecord/lib/arel/collectors/composite.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Arel
+  module Collectors
+    class Composite
+      def initialize(left, right)
+        @left = left
+        @right = right
+      end
+
+      def << str
+        left << str
+        right << str
+        self
+      end
+
+      def add_bind bind, &block
+        left.add_bind bind, &block
+        right.add_bind bind, &block
+        self
+      end
+
+      def value
+        [left.value, right.value]
+      end
+
+      protected
+
+      attr_reader :left, :right
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/plain_string.rb b/activerecord/lib/arel/collectors/plain_string.rb
new file mode 100644
index 0000000000..1e8d2a2152
--- /dev/null
+++ b/activerecord/lib/arel/collectors/plain_string.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+module Arel
+  module Collectors
+    class PlainString
+      def initialize
+        @str = ''.dup
+      end
+
+      def value
+        @str
+      end
+
+      def << str
+        @str << str
+        self
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/sql_string.rb b/activerecord/lib/arel/collectors/sql_string.rb
new file mode 100644
index 0000000000..bcb941f6d4
--- /dev/null
+++ b/activerecord/lib/arel/collectors/sql_string.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+require 'arel/collectors/plain_string'
+
+module Arel
+  module Collectors
+    class SQLString < PlainString
+      def initialize(*)
+        super
+        @bind_index = 1
+      end
+
+      def add_bind bind
+        self << yield(@bind_index)
+        @bind_index += 1
+        self
+      end
+
+      def compile bvs
+        value
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/substitute_binds.rb b/activerecord/lib/arel/collectors/substitute_binds.rb
new file mode 100644
index 0000000000..99d2215aaa
--- /dev/null
+++ b/activerecord/lib/arel/collectors/substitute_binds.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+module Arel
+  module Collectors
+    class SubstituteBinds
+      def initialize(quoter, delegate_collector)
+        @quoter = quoter
+        @delegate = delegate_collector
+      end
+
+      def << str
+        delegate << str
+        self
+      end
+
+      def add_bind bind
+        self << quoter.quote(bind)
+      end
+
+      def value
+        delegate.value
+      end
+
+      protected
+
+      attr_reader :quoter, :delegate
+    end
+  end
+end
diff --git a/activerecord/lib/arel/compatibility/wheres.rb b/activerecord/lib/arel/compatibility/wheres.rb
new file mode 100644
index 0000000000..3e60894bd8
--- /dev/null
+++ b/activerecord/lib/arel/compatibility/wheres.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+module Arel
+  module Compatibility # :nodoc:
+    class Wheres # :nodoc:
+      include Enumerable
+
+      module Value # :nodoc:
+        attr_accessor :visitor
+        def value
+          visitor.accept self
+        end
+
+        def name
+          super.to_sym
+        end
+      end
+
+      def initialize engine, collection
+        @engine     = engine
+        @collection = collection
+      end
+
+      def each
+        to_sql = Visitors::ToSql.new @engine
+
+        @collection.each { |c|
+          c.extend(Value)
+          c.visitor = to_sql
+          yield c
+        }
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/crud.rb b/activerecord/lib/arel/crud.rb
new file mode 100644
index 0000000000..2d10432205
--- /dev/null
+++ b/activerecord/lib/arel/crud.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+module Arel
+  ###
+  # FIXME hopefully we can remove this
+  module Crud
+    def compile_update values, pk
+      um = UpdateManager.new
+
+      if Nodes::SqlLiteral === values
+        relation = @ctx.from
+      else
+        relation = values.first.first.relation
+      end
+      um.key = pk
+      um.table relation
+      um.set values
+      um.take @ast.limit.expr if @ast.limit
+      um.order(*@ast.orders)
+      um.wheres = @ctx.wheres
+      um
+    end
+
+    def compile_insert values
+      im = create_insert
+      im.insert values
+      im
+    end
+
+    def create_insert
+      InsertManager.new
+    end
+
+    def compile_delete
+      dm = DeleteManager.new
+      dm.take @ast.limit.expr if @ast.limit
+      dm.wheres = @ctx.wheres
+      dm.from @ctx.froms
+      dm
+    end
+
+  end
+end
diff --git a/activerecord/lib/arel/delete_manager.rb b/activerecord/lib/arel/delete_manager.rb
new file mode 100644
index 0000000000..aee4511249
--- /dev/null
+++ b/activerecord/lib/arel/delete_manager.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+module Arel
+  class DeleteManager < Arel::TreeManager
+    def initialize
+      super
+      @ast = Nodes::DeleteStatement.new
+      @ctx = @ast
+    end
+
+    def from relation
+      @ast.relation = relation
+      self
+    end
+
+    def take limit
+      @ast.limit = Nodes::Limit.new(Nodes.build_quoted(limit)) if limit
+      self
+    end
+
+    def wheres= list
+      @ast.wheres = list
+    end
+  end
+end
diff --git a/activerecord/lib/arel/errors.rb b/activerecord/lib/arel/errors.rb
new file mode 100644
index 0000000000..86fbb80461
--- /dev/null
+++ b/activerecord/lib/arel/errors.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+module Arel
+  class ArelError < StandardError
+  end
+
+  class EmptyJoinError < ArelError
+  end
+end
diff --git a/activerecord/lib/arel/expressions.rb b/activerecord/lib/arel/expressions.rb
new file mode 100644
index 0000000000..612a0942f1
--- /dev/null
+++ b/activerecord/lib/arel/expressions.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+module Arel
+  module Expressions
+    def count distinct = false
+      Nodes::Count.new [self], distinct
+    end
+
+    def sum
+      Nodes::Sum.new [self]
+    end
+
+    def maximum
+      Nodes::Max.new [self]
+    end
+
+    def minimum
+      Nodes::Min.new [self]
+    end
+
+    def average
+      Nodes::Avg.new [self]
+    end
+
+    def extract field
+      Nodes::Extract.new [self], field
+    end
+
+  end
+end
diff --git a/activerecord/lib/arel/factory_methods.rb b/activerecord/lib/arel/factory_methods.rb
new file mode 100644
index 0000000000..6647c5ac44
--- /dev/null
+++ b/activerecord/lib/arel/factory_methods.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+module Arel
+  ###
+  # Methods for creating various nodes
+  module FactoryMethods
+    def create_true
+      Arel::Nodes::True.new
+    end
+
+    def create_false
+      Arel::Nodes::False.new
+    end
+
+    def create_table_alias relation, name
+      Nodes::TableAlias.new(relation, name)
+    end
+
+    def create_join to, constraint = nil, klass = Nodes::InnerJoin
+      klass.new(to, constraint)
+    end
+
+    def create_string_join to
+      create_join to, nil, Nodes::StringJoin
+    end
+
+    def create_and clauses
+      Nodes::And.new clauses
+    end
+
+    def create_on expr
+      Nodes::On.new expr
+    end
+
+    def grouping expr
+      Nodes::Grouping.new expr
+    end
+
+    ###
+    # Create a LOWER() function
+    def lower column
+      Nodes::NamedFunction.new 'LOWER', [Nodes.build_quoted(column)]
+    end
+  end
+end
diff --git a/activerecord/lib/arel/insert_manager.rb b/activerecord/lib/arel/insert_manager.rb
new file mode 100644
index 0000000000..dcbac6cb43
--- /dev/null
+++ b/activerecord/lib/arel/insert_manager.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+module Arel
+  class InsertManager < Arel::TreeManager
+    def initialize
+      super
+      @ast = Nodes::InsertStatement.new
+    end
+
+    def into table
+      @ast.relation = table
+      self
+    end
+
+    def columns; @ast.columns end
+    def values= val; @ast.values = val; end
+
+    def select select
+      @ast.select = select
+    end
+
+    def insert fields
+      return if fields.empty?
+
+      if String === fields
+        @ast.values = Nodes::SqlLiteral.new(fields)
+      else
+        @ast.relation ||= fields.first.first.relation
+
+        values = []
+
+        fields.each do |column, value|
+          @ast.columns << column
+          values << value
+        end
+        @ast.values = create_values values, @ast.columns
+      end
+      self
+    end
+
+    def create_values values, columns
+      Nodes::Values.new values, columns
+    end
+
+    def create_values_list(rows)
+      Nodes::ValuesList.new(rows)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/math.rb b/activerecord/lib/arel/math.rb
new file mode 100644
index 0000000000..9e6549b58f
--- /dev/null
+++ b/activerecord/lib/arel/math.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+module Arel
+  module Math
+    def *(other)
+      Arel::Nodes::Multiplication.new(self, other)
+    end
+
+    def +(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::Addition.new(self, other))
+    end
+
+    def -(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::Subtraction.new(self, other))
+    end
+
+    def /(other)
+      Arel::Nodes::Division.new(self, other)
+    end
+
+    def &(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseAnd.new(self, other))
+    end
+
+    def |(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseOr.new(self, other))
+    end
+
+    def ^(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseXor.new(self, other))
+    end
+
+    def <<(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseShiftLeft.new(self, other))
+    end
+
+    def >>(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseShiftRight.new(self, other))
+    end
+
+    def ~@
+      Arel::Nodes::BitwiseNot.new(self)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes.rb b/activerecord/lib/arel/nodes.rb
new file mode 100644
index 0000000000..8c6572dd6a
--- /dev/null
+++ b/activerecord/lib/arel/nodes.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+# node
+require 'arel/nodes/node'
+require 'arel/nodes/node_expression'
+require 'arel/nodes/select_statement'
+require 'arel/nodes/select_core'
+require 'arel/nodes/insert_statement'
+require 'arel/nodes/update_statement'
+require 'arel/nodes/bind_param'
+
+# terminal
+
+require 'arel/nodes/terminal'
+require 'arel/nodes/true'
+require 'arel/nodes/false'
+
+# unary
+require 'arel/nodes/unary'
+require 'arel/nodes/grouping'
+require 'arel/nodes/ascending'
+require 'arel/nodes/descending'
+require 'arel/nodes/unqualified_column'
+require 'arel/nodes/with'
+
+# binary
+require 'arel/nodes/binary'
+require 'arel/nodes/equality'
+require 'arel/nodes/in' # Why is this subclassed from equality?
+require 'arel/nodes/join_source'
+require 'arel/nodes/delete_statement'
+require 'arel/nodes/table_alias'
+require 'arel/nodes/infix_operation'
+require 'arel/nodes/unary_operation'
+require 'arel/nodes/over'
+require 'arel/nodes/matches'
+require 'arel/nodes/regexp'
+
+# nary
+require 'arel/nodes/and'
+
+# function
+# FIXME: Function + Alias can be rewritten as a Function and Alias node.
+# We should make Function a Unary node and deprecate the use of "aliaz"
+require 'arel/nodes/function'
+require 'arel/nodes/count'
+require 'arel/nodes/extract'
+require 'arel/nodes/values'
+require 'arel/nodes/values_list'
+require 'arel/nodes/named_function'
+
+# windows
+require 'arel/nodes/window'
+
+# conditional expressions
+require 'arel/nodes/case'
+
+# joins
+require 'arel/nodes/full_outer_join'
+require 'arel/nodes/inner_join'
+require 'arel/nodes/outer_join'
+require 'arel/nodes/right_outer_join'
+require 'arel/nodes/string_join'
+
+require 'arel/nodes/sql_literal'
+
+require 'arel/nodes/casted'
diff --git a/activerecord/lib/arel/nodes/and.rb b/activerecord/lib/arel/nodes/and.rb
new file mode 100644
index 0000000000..1e2f61cf43
--- /dev/null
+++ b/activerecord/lib/arel/nodes/and.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class And < Arel::Nodes::Node
+      attr_reader :children
+
+      def initialize children
+        super()
+        @children = children
+      end
+
+      def left
+        children.first
+      end
+
+      def right
+        children[1]
+      end
+
+      def hash
+        children.hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.children == other.children
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/ascending.rb b/activerecord/lib/arel/nodes/ascending.rb
new file mode 100644
index 0000000000..adadab55e4
--- /dev/null
+++ b/activerecord/lib/arel/nodes/ascending.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Ascending < Ordering
+
+      def reverse
+        Descending.new(expr)
+      end
+
+      def direction
+        :asc
+      end
+
+      def ascending?
+        true
+      end
+
+      def descending?
+        false
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/binary.rb b/activerecord/lib/arel/nodes/binary.rb
new file mode 100644
index 0000000000..a86d4e4696
--- /dev/null
+++ b/activerecord/lib/arel/nodes/binary.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Binary < Arel::Nodes::NodeExpression
+      attr_accessor :left, :right
+
+      def initialize left, right
+        super()
+        @left  = left
+        @right = right
+      end
+
+      def initialize_copy other
+        super
+        @left  = @left.clone if @left
+        @right = @right.clone if @right
+      end
+
+      def hash
+        [self.class, @left, @right].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.left == other.left &&
+          self.right == other.right
+      end
+      alias :== :eql?
+    end
+
+    %w{
+      As
+      Assignment
+      Between
+      GreaterThan
+      GreaterThanOrEqual
+      Join
+      LessThan
+      LessThanOrEqual
+      NotEqual
+      NotIn
+      Or
+      Union
+      UnionAll
+      Intersect
+      Except
+    }.each do |name|
+      const_set name, Class.new(Binary)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/bind_param.rb b/activerecord/lib/arel/nodes/bind_param.rb
new file mode 100644
index 0000000000..efa4f452d4
--- /dev/null
+++ b/activerecord/lib/arel/nodes/bind_param.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class BindParam < Node
+      attr_accessor :value
+
+      def initialize(value)
+        @value = value
+        super()
+      end
+
+      def hash
+        [self.class, self.value].hash
+      end
+
+      def eql?(other)
+        other.is_a?(BindParam) &&
+          value == other.value
+      end
+      alias :== :eql?
+
+      def nil?
+        value.nil?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/case.rb b/activerecord/lib/arel/nodes/case.rb
new file mode 100644
index 0000000000..50ea1e0be2
--- /dev/null
+++ b/activerecord/lib/arel/nodes/case.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Case < Arel::Nodes::Node
+      attr_accessor :case, :conditions, :default
+
+      def initialize expression = nil, default = nil
+        @case = expression
+        @conditions = []
+        @default = default
+      end
+
+      def when condition, expression = nil
+        @conditions << When.new(Nodes.build_quoted(condition), expression)
+        self
+      end
+
+      def then expression
+        @conditions.last.right = Nodes.build_quoted(expression)
+        self
+      end
+
+      def else expression
+        @default = Else.new Nodes.build_quoted(expression)
+        self
+      end
+
+      def initialize_copy other
+        super
+        @case = @case.clone if @case
+        @conditions = @conditions.map { |x| x.clone }
+        @default = @default.clone if @default
+      end
+
+      def hash
+        [@case, @conditions, @default].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.case == other.case &&
+          self.conditions == other.conditions &&
+          self.default == other.default
+      end
+      alias :== :eql?
+    end
+
+    class When < Binary # :nodoc:
+    end
+
+    class Else < Unary # :nodoc:
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/casted.rb b/activerecord/lib/arel/nodes/casted.rb
new file mode 100644
index 0000000000..f945063dd2
--- /dev/null
+++ b/activerecord/lib/arel/nodes/casted.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Casted < Arel::Nodes::NodeExpression # :nodoc:
+      attr_reader :val, :attribute
+      def initialize val, attribute
+        @val       = val
+        @attribute = attribute
+        super()
+      end
+
+      def nil?; @val.nil?; end
+
+      def hash
+        [self.class, val, attribute].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+            self.val == other.val &&
+            self.attribute == other.attribute
+      end
+      alias :== :eql?
+    end
+
+    class Quoted < Arel::Nodes::Unary # :nodoc:
+      alias :val :value
+      def nil?; val.nil?; end
+    end
+
+    def self.build_quoted other, attribute = nil
+      case other
+        when Arel::Nodes::Node, Arel::Attributes::Attribute, Arel::Table, Arel::Nodes::BindParam, Arel::SelectManager, Arel::Nodes::Quoted, Arel::Nodes::SqlLiteral
+          other
+        else
+          case attribute
+            when Arel::Attributes::Attribute
+              Casted.new other, attribute
+            else
+              Quoted.new other
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/count.rb b/activerecord/lib/arel/nodes/count.rb
new file mode 100644
index 0000000000..4dd9be453f
--- /dev/null
+++ b/activerecord/lib/arel/nodes/count.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Count < Arel::Nodes::Function
+      include Math
+
+      def initialize expr, distinct = false, aliaz = nil
+        super(expr, aliaz)
+        @distinct = distinct
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/delete_statement.rb b/activerecord/lib/arel/nodes/delete_statement.rb
new file mode 100644
index 0000000000..063a5341e5
--- /dev/null
+++ b/activerecord/lib/arel/nodes/delete_statement.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class DeleteStatement < Arel::Nodes::Node
+      attr_accessor :left, :right
+      attr_accessor :limit
+
+      alias :relation :left
+      alias :relation= :left=
+      alias :wheres :right
+      alias :wheres= :right=
+
+      def initialize relation = nil, wheres = []
+        super()
+        @left = relation
+        @right = wheres
+      end
+
+      def initialize_copy other
+        super
+        @left  = @left.clone if @left
+        @right = @right.clone if @right
+      end
+
+      def hash
+        [self.class, @left, @right].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.left == other.left &&
+          self.right == other.right
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/descending.rb b/activerecord/lib/arel/nodes/descending.rb
new file mode 100644
index 0000000000..d7261ab583
--- /dev/null
+++ b/activerecord/lib/arel/nodes/descending.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Descending < Ordering
+
+      def reverse
+        Ascending.new(expr)
+      end
+
+      def direction
+        :desc
+      end
+
+      def ascending?
+        false
+      end
+
+      def descending?
+        true
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/equality.rb b/activerecord/lib/arel/nodes/equality.rb
new file mode 100644
index 0000000000..ef44725e24
--- /dev/null
+++ b/activerecord/lib/arel/nodes/equality.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Equality < Arel::Nodes::Binary
+      def operator; :== end
+      alias :operand1 :left
+      alias :operand2 :right
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/extract.rb b/activerecord/lib/arel/nodes/extract.rb
new file mode 100644
index 0000000000..fdf3004c6a
--- /dev/null
+++ b/activerecord/lib/arel/nodes/extract.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Extract < Arel::Nodes::Unary
+      attr_accessor :field
+
+      def initialize expr, field
+        super(expr)
+        @field = field
+      end
+
+      def hash
+        super ^ @field.hash
+      end
+
+      def eql? other
+        super &&
+          self.field == other.field
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/false.rb b/activerecord/lib/arel/nodes/false.rb
new file mode 100644
index 0000000000..58132a2f90
--- /dev/null
+++ b/activerecord/lib/arel/nodes/false.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class False < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/full_outer_join.rb b/activerecord/lib/arel/nodes/full_outer_join.rb
new file mode 100644
index 0000000000..12a02d8cd9
--- /dev/null
+++ b/activerecord/lib/arel/nodes/full_outer_join.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class FullOuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/function.rb b/activerecord/lib/arel/nodes/function.rb
new file mode 100644
index 0000000000..b3bf8f3e51
--- /dev/null
+++ b/activerecord/lib/arel/nodes/function.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Function < Arel::Nodes::NodeExpression
+      include Arel::WindowPredications
+      attr_accessor :expressions, :alias, :distinct
+
+      def initialize expr, aliaz = nil
+        super()
+        @expressions = expr
+        @alias       = aliaz && SqlLiteral.new(aliaz)
+        @distinct    = false
+      end
+
+      def as aliaz
+        self.alias = SqlLiteral.new(aliaz)
+        self
+      end
+
+      def hash
+        [@expressions, @alias, @distinct].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.expressions == other.expressions &&
+          self.alias == other.alias &&
+          self.distinct == other.distinct
+      end
+      alias :== :eql?
+
+    end
+
+    %w{
+      Sum
+      Exists
+      Max
+      Min
+      Avg
+    }.each do |name|
+      const_set(name, Class.new(Function))
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/grouping.rb b/activerecord/lib/arel/nodes/grouping.rb
new file mode 100644
index 0000000000..ffe66654ce
--- /dev/null
+++ b/activerecord/lib/arel/nodes/grouping.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Grouping < Unary
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/in.rb b/activerecord/lib/arel/nodes/in.rb
new file mode 100644
index 0000000000..30cd771c40
--- /dev/null
+++ b/activerecord/lib/arel/nodes/in.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class In < Equality
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/infix_operation.rb b/activerecord/lib/arel/nodes/infix_operation.rb
new file mode 100644
index 0000000000..4eb7c5356f
--- /dev/null
+++ b/activerecord/lib/arel/nodes/infix_operation.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+
+    class InfixOperation < Binary
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::OrderPredications
+      include Arel::AliasPredication
+      include Arel::Math
+
+      attr_reader :operator
+
+      def initialize operator, left, right
+        super(left, right)
+        @operator = operator
+      end
+    end
+
+    class Multiplication < InfixOperation
+      def initialize left, right
+        super(:*, left, right)
+      end
+    end
+
+    class Division < InfixOperation
+      def initialize left, right
+        super(:/, left, right)
+      end
+    end
+
+    class Addition < InfixOperation
+      def initialize left, right
+        super(:+, left, right)
+      end
+    end
+
+    class Subtraction < InfixOperation
+      def initialize left, right
+        super(:-, left, right)
+      end
+    end
+
+    class Concat < InfixOperation
+      def initialize left, right
+        super('||', left, right)
+      end
+    end
+
+    class BitwiseAnd < InfixOperation
+      def initialize left, right
+        super(:&, left, right)
+      end
+    end
+
+    class BitwiseOr < InfixOperation
+      def initialize left, right
+        super(:|, left, right)
+      end
+    end
+
+    class BitwiseXor < InfixOperation
+      def initialize left, right
+        super(:^, left, right)
+      end
+    end
+
+    class BitwiseShiftLeft < InfixOperation
+      def initialize left, right
+        super(:<<, left, right)
+      end
+    end
+
+    class BitwiseShiftRight < InfixOperation
+      def initialize left, right
+        super(:>>, left, right)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/inner_join.rb b/activerecord/lib/arel/nodes/inner_join.rb
new file mode 100644
index 0000000000..4e398267c3
--- /dev/null
+++ b/activerecord/lib/arel/nodes/inner_join.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class InnerJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/insert_statement.rb b/activerecord/lib/arel/nodes/insert_statement.rb
new file mode 100644
index 0000000000..72793bc1ad
--- /dev/null
+++ b/activerecord/lib/arel/nodes/insert_statement.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class InsertStatement < Arel::Nodes::Node
+      attr_accessor :relation, :columns, :values, :select
+
+      def initialize
+        super()
+        @relation = nil
+        @columns  = []
+        @values   = nil
+        @select   = nil
+      end
+
+      def initialize_copy other
+        super
+        @columns = @columns.clone
+        @values =  @values.clone if @values
+        @select =  @select.clone if @select
+      end
+
+      def hash
+        [@relation, @columns, @values, @select].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.columns == other.columns &&
+          self.select == other.select &&
+          self.values == other.values
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/join_source.rb b/activerecord/lib/arel/nodes/join_source.rb
new file mode 100644
index 0000000000..428ce8183e
--- /dev/null
+++ b/activerecord/lib/arel/nodes/join_source.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    ###
+    # Class that represents a join source
+    #
+    #   http://www.sqlite.org/syntaxdiagrams.html#join-source
+
+    class JoinSource < Arel::Nodes::Binary
+      def initialize single_source, joinop = []
+        super
+      end
+
+      def empty?
+        !left && right.empty?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/matches.rb b/activerecord/lib/arel/nodes/matches.rb
new file mode 100644
index 0000000000..3ad3850a8e
--- /dev/null
+++ b/activerecord/lib/arel/nodes/matches.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Matches < Binary
+      attr_reader :escape
+      attr_accessor :case_sensitive
+
+      def initialize(left, right, escape = nil, case_sensitive = false)
+        super(left, right)
+        @escape = escape && Nodes.build_quoted(escape)
+        @case_sensitive = case_sensitive
+      end
+    end
+
+    class DoesNotMatch < Matches; end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/named_function.rb b/activerecord/lib/arel/nodes/named_function.rb
new file mode 100644
index 0000000000..173838a7fd
--- /dev/null
+++ b/activerecord/lib/arel/nodes/named_function.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class NamedFunction < Arel::Nodes::Function
+      attr_accessor :name
+
+      def initialize name, expr, aliaz = nil
+        super(expr, aliaz)
+        @name = name
+      end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql? other
+        super && self.name == other.name
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/node.rb b/activerecord/lib/arel/nodes/node.rb
new file mode 100644
index 0000000000..d2e6313dda
--- /dev/null
+++ b/activerecord/lib/arel/nodes/node.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    ###
+    # Abstract base class for all AST nodes
+    class Node
+      include Arel::FactoryMethods
+      include Enumerable
+
+      if $DEBUG
+        def _caller
+          @caller
+        end
+
+        def initialize
+          @caller = caller.dup
+        end
+      end
+
+      ###
+      # Factory method to create a Nodes::Not node that has the recipient of
+      # the caller as a child.
+      def not
+        Nodes::Not.new self
+      end
+
+      ###
+      # Factory method to create a Nodes::Grouping node that has an Nodes::Or
+      # node as a child.
+      def or right
+        Nodes::Grouping.new Nodes::Or.new(self, right)
+      end
+
+      ###
+      # Factory method to create an Nodes::And node.
+      def and right
+        Nodes::And.new [self, right]
+      end
+
+      # FIXME: this method should go away.  I don't like people calling
+      # to_sql on non-head nodes.  This forces us to walk the AST until we
+      # can find a node that has a "relation" member.
+      #
+      # Maybe we should just use `Table.engine`?  :'(
+      def to_sql engine = Table.engine
+        collector = Arel::Collectors::SQLString.new
+        collector = engine.connection.visitor.accept self, collector
+        collector.value
+      end
+
+      # Iterate through AST, nodes will be yielded depth-first
+      def each &block
+        return enum_for(:each) unless block_given?
+
+        ::Arel::Visitors::DepthFirst.new(block).accept self
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/node_expression.rb b/activerecord/lib/arel/nodes/node_expression.rb
new file mode 100644
index 0000000000..c4d4c8f428
--- /dev/null
+++ b/activerecord/lib/arel/nodes/node_expression.rb
@@ -0,0 +1,11 @@
+module Arel
+  module Nodes
+    class NodeExpression < Arel::Nodes::Node
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+      include Arel::Math
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/outer_join.rb b/activerecord/lib/arel/nodes/outer_join.rb
new file mode 100644
index 0000000000..c568655fe6
--- /dev/null
+++ b/activerecord/lib/arel/nodes/outer_join.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class OuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/over.rb b/activerecord/lib/arel/nodes/over.rb
new file mode 100644
index 0000000000..47a34e69ea
--- /dev/null
+++ b/activerecord/lib/arel/nodes/over.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+
+    class Over < Binary
+      include Arel::AliasPredication
+
+      def initialize(left, right = nil)
+        super(left, right)
+      end
+
+      def operator; 'OVER' end
+    end
+
+  end
+end
\ No newline at end of file
diff --git a/activerecord/lib/arel/nodes/regexp.rb b/activerecord/lib/arel/nodes/regexp.rb
new file mode 100644
index 0000000000..8a76185ef0
--- /dev/null
+++ b/activerecord/lib/arel/nodes/regexp.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Regexp < Binary
+      attr_accessor :case_sensitive
+
+      def initialize(left, right, case_sensitive = true)
+        super(left, right)
+        @case_sensitive = case_sensitive
+      end
+    end
+
+    class NotRegexp < Regexp; end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/right_outer_join.rb b/activerecord/lib/arel/nodes/right_outer_join.rb
new file mode 100644
index 0000000000..04ab31ebf0
--- /dev/null
+++ b/activerecord/lib/arel/nodes/right_outer_join.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class RightOuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/select_core.rb b/activerecord/lib/arel/nodes/select_core.rb
new file mode 100644
index 0000000000..fa1c026107
--- /dev/null
+++ b/activerecord/lib/arel/nodes/select_core.rb
@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class SelectCore < Arel::Nodes::Node
+      attr_accessor :top, :projections, :wheres, :groups, :windows
+      attr_accessor :havings, :source, :set_quantifier
+
+      def initialize
+        super()
+        @source         = JoinSource.new nil
+        @top            = nil
+
+        # https://ronsavage.github.io/SQL/sql-92.bnf.html#set%20quantifier
+        @set_quantifier = nil
+        @projections    = []
+        @wheres         = []
+        @groups         = []
+        @havings        = []
+        @windows        = []
+      end
+
+      def from
+        @source.left
+      end
+
+      def from= value
+        @source.left = value
+      end
+
+      alias :froms= :from=
+      alias :froms :from
+
+      def initialize_copy other
+        super
+        @source      = @source.clone if @source
+        @projections = @projections.clone
+        @wheres      = @wheres.clone
+        @groups      = @groups.clone
+        @havings     = @havings.clone
+        @windows     = @windows.clone
+      end
+
+      def hash
+        [
+          @source, @top, @set_quantifier, @projections,
+          @wheres, @groups, @havings, @windows
+        ].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.source == other.source &&
+          self.top == other.top &&
+          self.set_quantifier == other.set_quantifier &&
+          self.projections == other.projections &&
+          self.wheres == other.wheres &&
+          self.groups == other.groups &&
+          self.havings == other.havings &&
+          self.windows == other.windows
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/select_statement.rb b/activerecord/lib/arel/nodes/select_statement.rb
new file mode 100644
index 0000000000..79176d4be5
--- /dev/null
+++ b/activerecord/lib/arel/nodes/select_statement.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class SelectStatement < Arel::Nodes::NodeExpression
+      attr_reader :cores
+      attr_accessor :limit, :orders, :lock, :offset, :with
+
+      def initialize cores = [SelectCore.new]
+        super()
+        @cores          = cores
+        @orders         = []
+        @limit          = nil
+        @lock           = nil
+        @offset         = nil
+        @with           = nil
+      end
+
+      def initialize_copy other
+        super
+        @cores  = @cores.map { |x| x.clone }
+        @orders = @orders.map { |x| x.clone }
+      end
+
+      def hash
+        [@cores, @orders, @limit, @lock, @offset, @with].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.cores == other.cores &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.lock == other.lock &&
+          self.offset == other.offset &&
+          self.with == other.with
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/sql_literal.rb b/activerecord/lib/arel/nodes/sql_literal.rb
new file mode 100644
index 0000000000..73575a7d49
--- /dev/null
+++ b/activerecord/lib/arel/nodes/sql_literal.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class SqlLiteral < String
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+
+      def encode_with(coder)
+        coder.scalar = self.to_s
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/string_join.rb b/activerecord/lib/arel/nodes/string_join.rb
new file mode 100644
index 0000000000..21d6845c45
--- /dev/null
+++ b/activerecord/lib/arel/nodes/string_join.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class StringJoin < Arel::Nodes::Join
+      def initialize left, right = nil
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/table_alias.rb b/activerecord/lib/arel/nodes/table_alias.rb
new file mode 100644
index 0000000000..78deb175b6
--- /dev/null
+++ b/activerecord/lib/arel/nodes/table_alias.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class TableAlias < Arel::Nodes::Binary
+      alias :name :right
+      alias :relation :left
+      alias :table_alias :name
+
+      def [] name
+        Attribute.new(self, name)
+      end
+
+      def table_name
+        relation.respond_to?(:name) ? relation.name : name
+      end
+
+      def type_cast_for_database(*args)
+        relation.type_cast_for_database(*args)
+      end
+
+      def able_to_type_cast?
+        relation.respond_to?(:able_to_type_cast?) && relation.able_to_type_cast?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/terminal.rb b/activerecord/lib/arel/nodes/terminal.rb
new file mode 100644
index 0000000000..3a1cd7f0e1
--- /dev/null
+++ b/activerecord/lib/arel/nodes/terminal.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Distinct < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/true.rb b/activerecord/lib/arel/nodes/true.rb
new file mode 100644
index 0000000000..fdb8ed2095
--- /dev/null
+++ b/activerecord/lib/arel/nodes/true.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class True < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unary.rb b/activerecord/lib/arel/nodes/unary.rb
new file mode 100644
index 0000000000..e458d87ab3
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unary.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Unary < Arel::Nodes::NodeExpression
+      attr_accessor :expr
+      alias :value :expr
+
+      def initialize expr
+        super()
+        @expr = expr
+      end
+
+      def hash
+        @expr.hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.expr == other.expr
+      end
+      alias :== :eql?
+    end
+
+    %w{
+      Bin
+      Cube
+      DistinctOn
+      Group
+      GroupingElement
+      GroupingSet
+      Lateral
+      Limit
+      Lock
+      Not
+      Offset
+      On
+      Ordering
+      RollUp
+      Top
+    }.each do |name|
+      const_set(name, Class.new(Unary))
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unary_operation.rb b/activerecord/lib/arel/nodes/unary_operation.rb
new file mode 100644
index 0000000000..be4e270e76
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unary_operation.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+
+    class UnaryOperation < Unary
+      attr_reader :operator
+
+      def initialize operator, operand
+        super(operand)
+        @operator = operator
+      end
+    end
+
+    class BitwiseNot < UnaryOperation
+      def initialize operand
+        super(:~, operand)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unqualified_column.rb b/activerecord/lib/arel/nodes/unqualified_column.rb
new file mode 100644
index 0000000000..f9017238c8
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unqualified_column.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class UnqualifiedColumn < Arel::Nodes::Unary
+      alias :attribute :expr
+      alias :attribute= :expr=
+
+      def relation
+        @expr.relation
+      end
+
+      def column
+        @expr.column
+      end
+
+      def name
+        @expr.name
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/update_statement.rb b/activerecord/lib/arel/nodes/update_statement.rb
new file mode 100644
index 0000000000..286f0bd3ce
--- /dev/null
+++ b/activerecord/lib/arel/nodes/update_statement.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class UpdateStatement < Arel::Nodes::Node
+      attr_accessor :relation, :wheres, :values, :orders, :limit
+      attr_accessor :key
+
+      def initialize
+        @relation = nil
+        @wheres   = []
+        @values   = []
+        @orders   = []
+        @limit    = nil
+        @key      = nil
+      end
+
+      def initialize_copy other
+        super
+        @wheres = @wheres.clone
+        @values = @values.clone
+      end
+
+      def hash
+        [@relation, @wheres, @values, @orders, @limit, @key].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.wheres == other.wheres &&
+          self.values == other.values &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.key == other.key
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/values.rb b/activerecord/lib/arel/nodes/values.rb
new file mode 100644
index 0000000000..b32d5063a2
--- /dev/null
+++ b/activerecord/lib/arel/nodes/values.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Values < Arel::Nodes::Binary
+      alias :expressions :left
+      alias :expressions= :left=
+      alias :columns :right
+      alias :columns= :right=
+
+      def initialize exprs, columns = []
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/values_list.rb b/activerecord/lib/arel/nodes/values_list.rb
new file mode 100644
index 0000000000..89cea1790d
--- /dev/null
+++ b/activerecord/lib/arel/nodes/values_list.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class ValuesList < Node
+      attr_reader :rows
+
+      def initialize(rows)
+        @rows = rows
+        super()
+      end
+
+      def hash
+        @rows.hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.rows == other.rows
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/window.rb b/activerecord/lib/arel/nodes/window.rb
new file mode 100644
index 0000000000..23a005daba
--- /dev/null
+++ b/activerecord/lib/arel/nodes/window.rb
@@ -0,0 +1,125 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class Window < Arel::Nodes::Node
+      attr_accessor :orders, :framing, :partitions
+
+      def initialize
+        @orders = []
+        @partitions = []
+        @framing = nil
+      end
+
+      def order *expr
+        # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+        @orders.concat expr.map { |x|
+          String === x || Symbol === x ? Nodes::SqlLiteral.new(x.to_s) : x
+        }
+        self
+      end
+
+      def partition *expr
+        # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+        @partitions.concat expr.map { |x|
+          String === x || Symbol === x ? Nodes::SqlLiteral.new(x.to_s) : x
+        }
+        self
+      end
+
+      def frame(expr)
+        @framing = expr
+      end
+
+      def rows(expr = nil)
+        if @framing
+          Rows.new(expr)
+        else
+          frame(Rows.new(expr))
+        end
+      end
+
+      def range(expr = nil)
+        if @framing
+          Range.new(expr)
+        else
+          frame(Range.new(expr))
+        end
+      end
+
+      def initialize_copy other
+        super
+        @orders = @orders.map { |x| x.clone }
+      end
+
+      def hash
+        [@orders, @framing].hash
+      end
+
+      def eql? other
+        self.class == other.class &&
+          self.orders == other.orders &&
+          self.framing == other.framing &&
+          self.partitions == other.partitions
+      end
+      alias :== :eql?
+    end
+
+    class NamedWindow < Window
+      attr_accessor :name
+
+      def initialize name
+        super()
+        @name = name
+      end
+
+      def initialize_copy other
+        super
+        @name = other.name.clone
+      end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql? other
+        super && self.name == other.name
+      end
+      alias :== :eql?
+    end
+
+    class Rows < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class Range < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class CurrentRow < Node
+      def hash
+        self.class.hash
+      end
+
+      def eql? other
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+
+    class Preceding < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class Following < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/with.rb b/activerecord/lib/arel/nodes/with.rb
new file mode 100644
index 0000000000..def7840ea3
--- /dev/null
+++ b/activerecord/lib/arel/nodes/with.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+module Arel
+  module Nodes
+    class With < Arel::Nodes::Unary
+      alias children expr
+    end
+
+    class WithRecursive < With; end
+  end
+end
+
diff --git a/activerecord/lib/arel/order_predications.rb b/activerecord/lib/arel/order_predications.rb
new file mode 100644
index 0000000000..d84be82bb6
--- /dev/null
+++ b/activerecord/lib/arel/order_predications.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+module Arel
+  module OrderPredications
+
+    def asc
+      Nodes::Ascending.new self
+    end
+
+    def desc
+      Nodes::Descending.new self
+    end
+
+  end
+end
diff --git a/activerecord/lib/arel/predications.rb b/activerecord/lib/arel/predications.rb
new file mode 100644
index 0000000000..799c7c67b8
--- /dev/null
+++ b/activerecord/lib/arel/predications.rb
@@ -0,0 +1,240 @@
+# frozen_string_literal: true
+module Arel
+  module Predications
+    def not_eq other
+      Nodes::NotEqual.new self, quoted_node(other)
+    end
+
+    def not_eq_any others
+      grouping_any :not_eq, others
+    end
+
+    def not_eq_all others
+      grouping_all :not_eq, others
+    end
+
+    def eq other
+      Nodes::Equality.new self, quoted_node(other)
+    end
+
+    def eq_any others
+      grouping_any :eq, others
+    end
+
+    def eq_all others
+      grouping_all :eq, quoted_array(others)
+    end
+
+    def between other
+      if equals_quoted?(other.begin, -Float::INFINITY)
+        if equals_quoted?(other.end, Float::INFINITY)
+          not_in([])
+        elsif other.exclude_end?
+          lt(other.end)
+        else
+          lteq(other.end)
+        end
+      elsif equals_quoted?(other.end, Float::INFINITY)
+        gteq(other.begin)
+      elsif other.exclude_end?
+        gteq(other.begin).and(lt(other.end))
+      else
+        left = quoted_node(other.begin)
+        right = quoted_node(other.end)
+        Nodes::Between.new(self, left.and(right))
+      end
+    end
+
+    def in other
+      case other
+      when Arel::SelectManager
+        Arel::Nodes::In.new(self, other.ast)
+      when Range
+        if $VERBOSE
+          warn <<-eowarn
+Passing a range to `#in` is deprecated. Call `#between`, instead.
+          eowarn
+        end
+        between(other)
+      when Enumerable
+        Nodes::In.new self, quoted_array(other)
+      else
+        Nodes::In.new self, quoted_node(other)
+      end
+    end
+
+    def in_any others
+      grouping_any :in, others
+    end
+
+    def in_all others
+      grouping_all :in, others
+    end
+
+    def not_between other
+      if equals_quoted?(other.begin, -Float::INFINITY)
+        if equals_quoted?(other.end, Float::INFINITY)
+          self.in([])
+        elsif other.exclude_end?
+          gteq(other.end)
+        else
+          gt(other.end)
+        end
+      elsif equals_quoted?(other.end, Float::INFINITY)
+        lt(other.begin)
+      else
+        left = lt(other.begin)
+        right = if other.exclude_end?
+          gteq(other.end)
+        else
+          gt(other.end)
+        end
+        left.or(right)
+      end
+    end
+
+    def not_in other
+      case other
+      when Arel::SelectManager
+        Arel::Nodes::NotIn.new(self, other.ast)
+      when Range
+        if $VERBOSE
+          warn <<-eowarn
+Passing a range to `#not_in` is deprecated. Call `#not_between`, instead.
+          eowarn
+        end
+        not_between(other)
+      when Enumerable
+        Nodes::NotIn.new self, quoted_array(other)
+      else
+        Nodes::NotIn.new self, quoted_node(other)
+      end
+    end
+
+    def not_in_any others
+      grouping_any :not_in, others
+    end
+
+    def not_in_all others
+      grouping_all :not_in, others
+    end
+
+    def matches other, escape = nil, case_sensitive = false
+      Nodes::Matches.new self, quoted_node(other), escape, case_sensitive
+    end
+
+    def matches_regexp other, case_sensitive = true
+      Nodes::Regexp.new self, quoted_node(other), case_sensitive
+    end
+
+    def matches_any others, escape = nil, case_sensitive = false
+      grouping_any :matches, others, escape, case_sensitive
+    end
+
+    def matches_all others, escape = nil, case_sensitive = false
+      grouping_all :matches, others, escape, case_sensitive
+    end
+
+    def does_not_match other, escape = nil, case_sensitive = false
+      Nodes::DoesNotMatch.new self, quoted_node(other), escape, case_sensitive
+    end
+
+    def does_not_match_regexp other, case_sensitive = true
+      Nodes::NotRegexp.new self, quoted_node(other), case_sensitive
+    end
+
+    def does_not_match_any others, escape = nil
+      grouping_any :does_not_match, others, escape
+    end
+
+    def does_not_match_all others, escape = nil
+      grouping_all :does_not_match, others, escape
+    end
+
+    def gteq right
+      Nodes::GreaterThanOrEqual.new self, quoted_node(right)
+    end
+
+    def gteq_any others
+      grouping_any :gteq, others
+    end
+
+    def gteq_all others
+      grouping_all :gteq, others
+    end
+
+    def gt right
+      Nodes::GreaterThan.new self, quoted_node(right)
+    end
+
+    def gt_any others
+      grouping_any :gt, others
+    end
+
+    def gt_all others
+      grouping_all :gt, others
+    end
+
+    def lt right
+      Nodes::LessThan.new self, quoted_node(right)
+    end
+
+    def lt_any others
+      grouping_any :lt, others
+    end
+
+    def lt_all others
+      grouping_all :lt, others
+    end
+
+    def lteq right
+      Nodes::LessThanOrEqual.new self, quoted_node(right)
+    end
+
+    def lteq_any others
+      grouping_any :lteq, others
+    end
+
+    def lteq_all others
+      grouping_all :lteq, others
+    end
+
+    def when right
+      Nodes::Case.new(self).when quoted_node(right)
+    end
+
+    def concat other
+      Nodes::Concat.new self, other
+    end
+
+    private
+
+    def grouping_any method_id, others, *extras
+      nodes = others.map {|expr| send(method_id, expr, *extras)}
+      Nodes::Grouping.new nodes.inject { |memo,node|
+        Nodes::Or.new(memo, node)
+      }
+    end
+
+    def grouping_all method_id, others, *extras
+      nodes = others.map {|expr| send(method_id, expr, *extras)}
+      Nodes::Grouping.new Nodes::And.new(nodes)
+    end
+
+    def quoted_node(other)
+      Nodes.build_quoted(other, self)
+    end
+
+    def quoted_array(others)
+      others.map { |v| quoted_node(v) }
+    end
+
+    def equals_quoted?(maybe_quoted, value)
+      if maybe_quoted.is_a?(Nodes::Quoted)
+        maybe_quoted.val == value
+      else
+        maybe_quoted == value
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/select_manager.rb b/activerecord/lib/arel/select_manager.rb
new file mode 100644
index 0000000000..0f3b0dc6a0
--- /dev/null
+++ b/activerecord/lib/arel/select_manager.rb
@@ -0,0 +1,272 @@
+# frozen_string_literal: true
+module Arel
+  class SelectManager < Arel::TreeManager
+    include Arel::Crud
+
+    STRING_OR_SYMBOL_CLASS = [Symbol, String]
+
+    def initialize table = nil
+      super()
+      @ast   = Nodes::SelectStatement.new
+      @ctx    = @ast.cores.last
+      from table
+    end
+
+    def initialize_copy other
+      super
+      @ctx = @ast.cores.last
+    end
+
+    def limit
+      @ast.limit && @ast.limit.expr
+    end
+    alias :taken :limit
+
+    def constraints
+      @ctx.wheres
+    end
+
+    def offset
+      @ast.offset && @ast.offset.expr
+    end
+
+    def skip amount
+      if amount
+        @ast.offset = Nodes::Offset.new(amount)
+      else
+        @ast.offset = nil
+      end
+      self
+    end
+    alias :offset= :skip
+
+    ###
+    # Produces an Arel::Nodes::Exists node
+    def exists
+      Arel::Nodes::Exists.new @ast
+    end
+
+    def as other
+      create_table_alias grouping(@ast), Nodes::SqlLiteral.new(other)
+    end
+
+    def lock locking = Arel.sql('FOR UPDATE')
+      case locking
+      when true
+        locking = Arel.sql('FOR UPDATE')
+      when Arel::Nodes::SqlLiteral
+      when String
+        locking = Arel.sql locking
+      end
+
+      @ast.lock = Nodes::Lock.new(locking)
+      self
+    end
+
+    def locked
+      @ast.lock
+    end
+
+    def on *exprs
+      @ctx.source.right.last.right = Nodes::On.new(collapse(exprs))
+      self
+    end
+
+    def group *columns
+      columns.each do |column|
+        # FIXME: backwards compat
+        column = Nodes::SqlLiteral.new(column) if String === column
+        column = Nodes::SqlLiteral.new(column.to_s) if Symbol === column
+
+        @ctx.groups.push Nodes::Group.new column
+      end
+      self
+    end
+
+    def from table
+      table = Nodes::SqlLiteral.new(table) if String === table
+
+      case table
+      when Nodes::Join
+        @ctx.source.right << table
+      else
+        @ctx.source.left = table
+      end
+
+      self
+    end
+
+    def froms
+      @ast.cores.map { |x| x.from }.compact
+    end
+
+    def join relation, klass = Nodes::InnerJoin
+      return self unless relation
+
+      case relation
+      when String, Nodes::SqlLiteral
+        raise EmptyJoinError if relation.empty?
+        klass = Nodes::StringJoin
+      end
+
+      @ctx.source.right << create_join(relation, nil, klass)
+      self
+    end
+
+    def outer_join relation
+      join(relation, Nodes::OuterJoin)
+    end
+
+    def having expr
+      @ctx.havings << expr
+      self
+    end
+
+    def window name
+      window = Nodes::NamedWindow.new(name)
+      @ctx.windows.push window
+      window
+    end
+
+    def project *projections
+      # FIXME: converting these to SQLLiterals is probably not good, but
+      # rails tests require it.
+      @ctx.projections.concat projections.map { |x|
+        STRING_OR_SYMBOL_CLASS.include?(x.class) ? Nodes::SqlLiteral.new(x.to_s) : x
+      }
+      self
+    end
+
+    def projections
+      @ctx.projections
+    end
+
+    def projections= projections
+      @ctx.projections = projections
+    end
+
+    def distinct(value = true)
+      if value
+        @ctx.set_quantifier = Arel::Nodes::Distinct.new
+      else
+        @ctx.set_quantifier = nil
+      end
+      self
+    end
+
+    def distinct_on(value)
+      if value
+        @ctx.set_quantifier = Arel::Nodes::DistinctOn.new(value)
+      else
+        @ctx.set_quantifier = nil
+      end
+      self
+    end
+
+    def order *expr
+      # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+      @ast.orders.concat expr.map { |x|
+        STRING_OR_SYMBOL_CLASS.include?(x.class) ? Nodes::SqlLiteral.new(x.to_s) : x
+      }
+      self
+    end
+
+    def orders
+      @ast.orders
+    end
+
+    def where_sql engine = Table.engine
+      return if @ctx.wheres.empty?
+
+      viz = Visitors::WhereSql.new(engine.connection.visitor, engine.connection)
+      Nodes::SqlLiteral.new viz.accept(@ctx, Collectors::SQLString.new).value
+    end
+
+    def union operation, other = nil
+      if other
+        node_class = Nodes.const_get("Union#{operation.to_s.capitalize}")
+      else
+        other = operation
+        node_class = Nodes::Union
+      end
+
+      node_class.new self.ast, other.ast
+    end
+
+    def intersect other
+      Nodes::Intersect.new ast, other.ast
+    end
+
+    def except other
+      Nodes::Except.new ast, other.ast
+    end
+    alias :minus :except
+
+    def lateral table_name = nil
+      base = table_name.nil? ? ast : as(table_name)
+      Nodes::Lateral.new(base)
+    end
+
+    def with *subqueries
+      if subqueries.first.is_a? Symbol
+        node_class = Nodes.const_get("With#{subqueries.shift.to_s.capitalize}")
+      else
+        node_class = Nodes::With
+      end
+      @ast.with = node_class.new(subqueries.flatten)
+
+      self
+    end
+
+    def take limit
+      if limit
+        @ast.limit = Nodes::Limit.new(limit)
+        @ctx.top   = Nodes::Top.new(limit)
+      else
+        @ast.limit = nil
+        @ctx.top   = nil
+      end
+      self
+    end
+    alias limit= take
+
+    def join_sources
+      @ctx.source.right
+    end
+
+    def source
+      @ctx.source
+    end
+
+    class Row < Struct.new(:data) # :nodoc:
+      def id
+        data['id']
+      end
+
+      def method_missing(name, *args)
+        name = name.to_s
+        return data[name] if data.key?(name)
+        super
+      end
+    end
+
+    private
+    def collapse exprs, existing = nil
+      exprs = exprs.unshift(existing.expr) if existing
+      exprs = exprs.compact.map { |expr|
+        if String === expr
+          # FIXME: Don't do this automatically
+          Arel.sql(expr)
+        else
+          expr
+        end
+      }
+
+      if exprs.length == 1
+        exprs.first
+      else
+        create_and exprs
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/table.rb b/activerecord/lib/arel/table.rb
new file mode 100644
index 0000000000..b3f2d79e5f
--- /dev/null
+++ b/activerecord/lib/arel/table.rb
@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+module Arel
+  class Table
+    include Arel::Crud
+    include Arel::FactoryMethods
+
+    @engine = nil
+    class << self; attr_accessor :engine; end
+
+    attr_accessor :name, :table_alias
+
+    # TableAlias and Table both have a #table_name which is the name of the underlying table
+    alias :table_name :name
+
+    def initialize(name, as: nil, type_caster: nil)
+      @name    = name.to_s
+      @type_caster = type_caster
+
+      # Sometime AR sends an :as parameter to table, to let the table know
+      # that it is an Alias.  We may want to override new, and return a
+      # TableAlias node?
+      if as.to_s == @name
+        as = nil
+      end
+      @table_alias = as
+    end
+
+    def alias name = "#{self.name}_2"
+      Nodes::TableAlias.new(self, name)
+    end
+
+    def from
+      SelectManager.new(self)
+    end
+
+    def join relation, klass = Nodes::InnerJoin
+      return from unless relation
+
+      case relation
+      when String, Nodes::SqlLiteral
+        raise EmptyJoinError if relation.empty?
+        klass = Nodes::StringJoin
+      end
+
+      from.join(relation, klass)
+    end
+
+    def outer_join relation
+      join(relation, Nodes::OuterJoin)
+    end
+
+    def group *columns
+      from.group(*columns)
+    end
+
+    def order *expr
+      from.order(*expr)
+    end
+
+    def where condition
+      from.where condition
+    end
+
+    def project *things
+      from.project(*things)
+    end
+
+    def take amount
+      from.take amount
+    end
+
+    def skip amount
+      from.skip amount
+    end
+
+    def having expr
+      from.having expr
+    end
+
+    def [] name
+      ::Arel::Attribute.new self, name
+    end
+
+    def hash
+      # Perf note: aliases and table alias is excluded from the hash
+      #  aliases can have a loop back to this table breaking hashes in parent
+      #  relations, for the vast majority of cases @name is unique to a query
+      @name.hash
+    end
+
+    def eql? other
+      self.class == other.class &&
+        self.name == other.name &&
+        self.table_alias == other.table_alias
+    end
+    alias :== :eql?
+
+    def type_cast_for_database(attribute_name, value)
+      type_caster.type_cast_for_database(attribute_name, value)
+    end
+
+    def able_to_type_cast?
+      !type_caster.nil?
+    end
+
+    protected
+
+    attr_reader :type_caster
+  end
+end
diff --git a/activerecord/lib/arel/tree_manager.rb b/activerecord/lib/arel/tree_manager.rb
new file mode 100644
index 0000000000..b237bf368d
--- /dev/null
+++ b/activerecord/lib/arel/tree_manager.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+module Arel
+  class TreeManager
+    include Arel::FactoryMethods
+
+    attr_reader :ast
+
+    def initialize
+      @ctx = nil
+    end
+
+    def to_dot
+      collector = Arel::Collectors::PlainString.new
+      collector = Visitors::Dot.new.accept @ast, collector
+      collector.value
+    end
+
+    def to_sql engine = Table.engine
+      collector = Arel::Collectors::SQLString.new
+      collector = engine.connection.visitor.accept @ast, collector
+      collector.value
+    end
+
+    def initialize_copy other
+      super
+      @ast = @ast.clone
+    end
+
+    def where expr
+      if Arel::TreeManager === expr
+        expr = expr.ast
+      end
+      @ctx.wheres << expr
+      self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/update_manager.rb b/activerecord/lib/arel/update_manager.rb
new file mode 100644
index 0000000000..eac414eafb
--- /dev/null
+++ b/activerecord/lib/arel/update_manager.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+module Arel
+  class UpdateManager < Arel::TreeManager
+    def initialize
+      super
+      @ast = Nodes::UpdateStatement.new
+      @ctx = @ast
+    end
+
+    def take limit
+      @ast.limit = Nodes::Limit.new(Nodes.build_quoted(limit)) if limit
+      self
+    end
+
+    def key= key
+      @ast.key = Nodes.build_quoted(key)
+    end
+
+    def key
+      @ast.key
+    end
+
+    def order *expr
+      @ast.orders = expr
+      self
+    end
+
+    ###
+    # UPDATE +table+
+    def table table
+      @ast.relation = table
+      self
+    end
+
+    def wheres= exprs
+      @ast.wheres = exprs
+    end
+
+    def where expr
+      @ast.wheres << expr
+      self
+    end
+
+    def set values
+      if String === values
+        @ast.values = [values]
+      else
+        @ast.values = values.map { |column,value|
+          Nodes::Assignment.new(
+            Nodes::UnqualifiedColumn.new(column),
+            value
+          )
+        }
+      end
+      self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors.rb b/activerecord/lib/arel/visitors.rb
new file mode 100644
index 0000000000..a3404cf992
--- /dev/null
+++ b/activerecord/lib/arel/visitors.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+require 'arel/visitors/visitor'
+require 'arel/visitors/depth_first'
+require 'arel/visitors/to_sql'
+require 'arel/visitors/sqlite'
+require 'arel/visitors/postgresql'
+require 'arel/visitors/mysql'
+require 'arel/visitors/mssql'
+require 'arel/visitors/oracle'
+require 'arel/visitors/oracle12'
+require 'arel/visitors/where_sql'
+require 'arel/visitors/dot'
+require 'arel/visitors/ibm_db'
+require 'arel/visitors/informix'
+
+module Arel
+  module Visitors
+  end
+end
diff --git a/activerecord/lib/arel/visitors/depth_first.rb b/activerecord/lib/arel/visitors/depth_first.rb
new file mode 100644
index 0000000000..b3bbc9bd40
--- /dev/null
+++ b/activerecord/lib/arel/visitors/depth_first.rb
@@ -0,0 +1,199 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class DepthFirst < Arel::Visitors::Visitor
+      def initialize block = nil
+        @block = block || Proc.new
+        super()
+      end
+
+      private
+
+      def visit o
+        super
+        @block.call o
+      end
+
+      def unary o
+        visit o.expr
+      end
+      alias :visit_Arel_Nodes_Else              :unary
+      alias :visit_Arel_Nodes_Group             :unary
+      alias :visit_Arel_Nodes_Cube              :unary
+      alias :visit_Arel_Nodes_RollUp            :unary
+      alias :visit_Arel_Nodes_GroupingSet       :unary
+      alias :visit_Arel_Nodes_GroupingElement   :unary
+      alias :visit_Arel_Nodes_Grouping          :unary
+      alias :visit_Arel_Nodes_Having            :unary
+      alias :visit_Arel_Nodes_Lateral           :unary
+      alias :visit_Arel_Nodes_Limit             :unary
+      alias :visit_Arel_Nodes_Not               :unary
+      alias :visit_Arel_Nodes_Offset            :unary
+      alias :visit_Arel_Nodes_On                :unary
+      alias :visit_Arel_Nodes_Ordering          :unary
+      alias :visit_Arel_Nodes_Ascending         :unary
+      alias :visit_Arel_Nodes_Descending        :unary
+      alias :visit_Arel_Nodes_Top               :unary
+      alias :visit_Arel_Nodes_UnqualifiedColumn :unary
+
+      def function o
+        visit o.expressions
+        visit o.alias
+        visit o.distinct
+      end
+      alias :visit_Arel_Nodes_Avg    :function
+      alias :visit_Arel_Nodes_Exists :function
+      alias :visit_Arel_Nodes_Max    :function
+      alias :visit_Arel_Nodes_Min    :function
+      alias :visit_Arel_Nodes_Sum    :function
+
+      def visit_Arel_Nodes_NamedFunction o
+        visit o.name
+        visit o.expressions
+        visit o.distinct
+        visit o.alias
+      end
+
+      def visit_Arel_Nodes_Count o
+        visit o.expressions
+        visit o.alias
+        visit o.distinct
+      end
+
+      def visit_Arel_Nodes_Case o
+        visit o.case
+        visit o.conditions
+        visit o.default
+      end
+
+      def nary o
+        o.children.each { |child| visit child}
+      end
+      alias :visit_Arel_Nodes_And :nary
+
+      def binary o
+        visit o.left
+        visit o.right
+      end
+      alias :visit_Arel_Nodes_As                 :binary
+      alias :visit_Arel_Nodes_Assignment         :binary
+      alias :visit_Arel_Nodes_Between            :binary
+      alias :visit_Arel_Nodes_Concat             :binary
+      alias :visit_Arel_Nodes_DeleteStatement    :binary
+      alias :visit_Arel_Nodes_DoesNotMatch       :binary
+      alias :visit_Arel_Nodes_Equality           :binary
+      alias :visit_Arel_Nodes_FullOuterJoin      :binary
+      alias :visit_Arel_Nodes_GreaterThan        :binary
+      alias :visit_Arel_Nodes_GreaterThanOrEqual :binary
+      alias :visit_Arel_Nodes_In                 :binary
+      alias :visit_Arel_Nodes_InfixOperation     :binary
+      alias :visit_Arel_Nodes_JoinSource         :binary
+      alias :visit_Arel_Nodes_InnerJoin          :binary
+      alias :visit_Arel_Nodes_LessThan           :binary
+      alias :visit_Arel_Nodes_LessThanOrEqual    :binary
+      alias :visit_Arel_Nodes_Matches            :binary
+      alias :visit_Arel_Nodes_NotEqual           :binary
+      alias :visit_Arel_Nodes_NotIn              :binary
+      alias :visit_Arel_Nodes_NotRegexp          :binary
+      alias :visit_Arel_Nodes_Or                 :binary
+      alias :visit_Arel_Nodes_OuterJoin          :binary
+      alias :visit_Arel_Nodes_Regexp             :binary
+      alias :visit_Arel_Nodes_RightOuterJoin     :binary
+      alias :visit_Arel_Nodes_TableAlias         :binary
+      alias :visit_Arel_Nodes_Values             :binary
+      alias :visit_Arel_Nodes_When               :binary
+
+      def visit_Arel_Nodes_StringJoin o
+        visit o.left
+      end
+
+      def visit_Arel_Attribute o
+        visit o.relation
+        visit o.name
+      end
+      alias :visit_Arel_Attributes_Integer :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Float :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_String :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Time :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Boolean :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Attribute :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Decimal :visit_Arel_Attribute
+
+      def visit_Arel_Table o
+        visit o.name
+      end
+
+      def terminal o
+      end
+      alias :visit_ActiveSupport_Multibyte_Chars :terminal
+      alias :visit_ActiveSupport_StringInquirer  :terminal
+      alias :visit_Arel_Nodes_Lock               :terminal
+      alias :visit_Arel_Nodes_Node               :terminal
+      alias :visit_Arel_Nodes_SqlLiteral         :terminal
+      alias :visit_Arel_Nodes_BindParam          :terminal
+      alias :visit_Arel_Nodes_Window             :terminal
+      alias :visit_Arel_Nodes_True               :terminal
+      alias :visit_Arel_Nodes_False              :terminal
+      alias :visit_BigDecimal                    :terminal
+      alias :visit_Bignum                        :terminal
+      alias :visit_Class                         :terminal
+      alias :visit_Date                          :terminal
+      alias :visit_DateTime                      :terminal
+      alias :visit_FalseClass                    :terminal
+      alias :visit_Fixnum                        :terminal
+      alias :visit_Float                         :terminal
+      alias :visit_Integer                       :terminal
+      alias :visit_NilClass                      :terminal
+      alias :visit_String                        :terminal
+      alias :visit_Symbol                        :terminal
+      alias :visit_Time                          :terminal
+      alias :visit_TrueClass                     :terminal
+
+      def visit_Arel_Nodes_InsertStatement o
+        visit o.relation
+        visit o.columns
+        visit o.values
+      end
+
+      def visit_Arel_Nodes_SelectCore o
+        visit o.projections
+        visit o.source
+        visit o.wheres
+        visit o.groups
+        visit o.windows
+        visit o.havings
+      end
+
+      def visit_Arel_Nodes_SelectStatement o
+        visit o.cores
+        visit o.orders
+        visit o.limit
+        visit o.lock
+        visit o.offset
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o
+        visit o.relation
+        visit o.values
+        visit o.wheres
+        visit o.orders
+        visit o.limit
+      end
+
+      def visit_Array o
+        o.each { |i| visit i }
+      end
+      alias :visit_Set :visit_Array
+
+      def visit_Hash o
+        o.each { |k,v| visit(k); visit(v) }
+      end
+
+      DISPATCH = dispatch_cache
+
+      def get_dispatch_cache
+        DISPATCH
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/dot.rb b/activerecord/lib/arel/visitors/dot.rb
new file mode 100644
index 0000000000..9aa22d33f6
--- /dev/null
+++ b/activerecord/lib/arel/visitors/dot.rb
@@ -0,0 +1,291 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class Dot < Arel::Visitors::Visitor
+      class Node # :nodoc:
+        attr_accessor :name, :id, :fields
+
+        def initialize name, id, fields = []
+          @name   = name
+          @id     = id
+          @fields = fields
+        end
+      end
+
+      class Edge < Struct.new :name, :from, :to # :nodoc:
+      end
+
+      def initialize
+        super()
+        @nodes      = []
+        @edges      = []
+        @node_stack = []
+        @edge_stack = []
+        @seen       = {}
+      end
+
+      def accept object, collector
+        visit object
+        collector << to_dot
+      end
+
+      private
+
+      def visit_Arel_Nodes_Ordering o
+        visit_edge o, "expr"
+      end
+
+      def visit_Arel_Nodes_TableAlias o
+        visit_edge o, "name"
+        visit_edge o, "relation"
+      end
+
+      def visit_Arel_Nodes_Count o
+        visit_edge o, "expressions"
+        visit_edge o, "distinct"
+      end
+
+      def visit_Arel_Nodes_Values o
+        visit_edge o, "expressions"
+      end
+
+      def visit_Arel_Nodes_StringJoin o
+        visit_edge o, "left"
+      end
+
+      def visit_Arel_Nodes_InnerJoin o
+        visit_edge o, "left"
+        visit_edge o, "right"
+      end
+      alias :visit_Arel_Nodes_FullOuterJoin  :visit_Arel_Nodes_InnerJoin
+      alias :visit_Arel_Nodes_OuterJoin      :visit_Arel_Nodes_InnerJoin
+      alias :visit_Arel_Nodes_RightOuterJoin :visit_Arel_Nodes_InnerJoin
+
+      def visit_Arel_Nodes_DeleteStatement o
+        visit_edge o, "relation"
+        visit_edge o, "wheres"
+      end
+
+      def unary o
+        visit_edge o, "expr"
+      end
+      alias :visit_Arel_Nodes_Group             :unary
+      alias :visit_Arel_Nodes_Cube              :unary
+      alias :visit_Arel_Nodes_RollUp            :unary
+      alias :visit_Arel_Nodes_GroupingSet       :unary
+      alias :visit_Arel_Nodes_GroupingElement   :unary
+      alias :visit_Arel_Nodes_Grouping          :unary
+      alias :visit_Arel_Nodes_Having            :unary
+      alias :visit_Arel_Nodes_Limit             :unary
+      alias :visit_Arel_Nodes_Not               :unary
+      alias :visit_Arel_Nodes_Offset            :unary
+      alias :visit_Arel_Nodes_On                :unary
+      alias :visit_Arel_Nodes_Top               :unary
+      alias :visit_Arel_Nodes_UnqualifiedColumn :unary
+      alias :visit_Arel_Nodes_Preceding         :unary
+      alias :visit_Arel_Nodes_Following         :unary
+      alias :visit_Arel_Nodes_Rows              :unary
+      alias :visit_Arel_Nodes_Range             :unary
+
+      def window o
+        visit_edge o, "partitions"
+        visit_edge o, "orders"
+        visit_edge o, "framing"
+      end
+      alias :visit_Arel_Nodes_Window            :window
+
+      def named_window o
+        visit_edge o, "partitions"
+        visit_edge o, "orders"
+        visit_edge o, "framing"
+        visit_edge o, "name"
+      end
+      alias :visit_Arel_Nodes_NamedWindow       :named_window
+
+      def function o
+        visit_edge o, "expressions"
+        visit_edge o, "distinct"
+        visit_edge o, "alias"
+      end
+      alias :visit_Arel_Nodes_Exists :function
+      alias :visit_Arel_Nodes_Min    :function
+      alias :visit_Arel_Nodes_Max    :function
+      alias :visit_Arel_Nodes_Avg    :function
+      alias :visit_Arel_Nodes_Sum    :function
+
+      def extract o
+        visit_edge o, "expressions"
+        visit_edge o, "alias"
+      end
+      alias :visit_Arel_Nodes_Extract :extract
+
+      def visit_Arel_Nodes_NamedFunction o
+        visit_edge o, "name"
+        visit_edge o, "expressions"
+        visit_edge o, "distinct"
+        visit_edge o, "alias"
+      end
+
+      def visit_Arel_Nodes_InsertStatement o
+        visit_edge o, "relation"
+        visit_edge o, "columns"
+        visit_edge o, "values"
+      end
+
+      def visit_Arel_Nodes_SelectCore o
+        visit_edge o, "source"
+        visit_edge o, "projections"
+        visit_edge o, "wheres"
+        visit_edge o,  "windows"
+      end
+
+      def visit_Arel_Nodes_SelectStatement o
+        visit_edge o, "cores"
+        visit_edge o, "limit"
+        visit_edge o, "orders"
+        visit_edge o, "offset"
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o
+        visit_edge o, "relation"
+        visit_edge o, "wheres"
+        visit_edge o, "values"
+      end
+
+      def visit_Arel_Table o
+        visit_edge o, "name"
+      end
+
+      def visit_Arel_Nodes_Casted o
+        visit_edge o, 'val'
+        visit_edge o, 'attribute'
+      end
+
+      def visit_Arel_Attribute o
+        visit_edge o, "relation"
+        visit_edge o, "name"
+      end
+      alias :visit_Arel_Attributes_Integer :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Float :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_String :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Time :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Boolean :visit_Arel_Attribute
+      alias :visit_Arel_Attributes_Attribute :visit_Arel_Attribute
+
+      def nary o
+        o.children.each_with_index do |x,i|
+          edge(i) { visit x }
+        end
+      end
+      alias :visit_Arel_Nodes_And :nary
+
+      def binary o
+        visit_edge o, "left"
+        visit_edge o, "right"
+      end
+      alias :visit_Arel_Nodes_As                 :binary
+      alias :visit_Arel_Nodes_Assignment         :binary
+      alias :visit_Arel_Nodes_Between            :binary
+      alias :visit_Arel_Nodes_Concat             :binary
+      alias :visit_Arel_Nodes_DoesNotMatch       :binary
+      alias :visit_Arel_Nodes_Equality           :binary
+      alias :visit_Arel_Nodes_GreaterThan        :binary
+      alias :visit_Arel_Nodes_GreaterThanOrEqual :binary
+      alias :visit_Arel_Nodes_In                 :binary
+      alias :visit_Arel_Nodes_JoinSource         :binary
+      alias :visit_Arel_Nodes_LessThan           :binary
+      alias :visit_Arel_Nodes_LessThanOrEqual    :binary
+      alias :visit_Arel_Nodes_Matches            :binary
+      alias :visit_Arel_Nodes_NotEqual           :binary
+      alias :visit_Arel_Nodes_NotIn              :binary
+      alias :visit_Arel_Nodes_Or                 :binary
+      alias :visit_Arel_Nodes_Over               :binary
+
+      def visit_String o
+        @node_stack.last.fields << o
+      end
+      alias :visit_Time :visit_String
+      alias :visit_Date :visit_String
+      alias :visit_DateTime :visit_String
+      alias :visit_NilClass :visit_String
+      alias :visit_TrueClass :visit_String
+      alias :visit_FalseClass :visit_String
+      alias :visit_Integer :visit_String
+      alias :visit_Fixnum :visit_String
+      alias :visit_BigDecimal :visit_String
+      alias :visit_Float :visit_String
+      alias :visit_Symbol :visit_String
+      alias :visit_Arel_Nodes_SqlLiteral :visit_String
+
+      def visit_Arel_Nodes_BindParam o; end
+
+      def visit_Hash o
+        o.each_with_index do |pair, i|
+          edge("pair_#{i}")   { visit pair }
+        end
+      end
+
+      def visit_Array o
+        o.each_with_index do |x,i|
+          edge(i) { visit x }
+        end
+      end
+      alias :visit_Set :visit_Array
+
+      def visit_edge o, method
+        edge(method) { visit o.send(method) }
+      end
+
+      def visit o
+        if node = @seen[o.object_id]
+          @edge_stack.last.to = node
+          return
+        end
+
+        node = Node.new(o.class.name, o.object_id)
+        @seen[node.id] = node
+        @nodes << node
+        with_node node do
+          super
+        end
+      end
+
+      def edge name
+        edge = Edge.new(name, @node_stack.last)
+        @edge_stack.push edge
+        @edges << edge
+        yield
+        @edge_stack.pop
+      end
+
+      def with_node node
+        if edge = @edge_stack.last
+          edge.to = node
+        end
+
+        @node_stack.push node
+        yield
+        @node_stack.pop
+      end
+
+      def quote string
+        string.to_s.gsub('"', '\"')
+      end
+
+      def to_dot
+        "digraph \"Arel\" {\nnode [width=0.375,height=0.25,shape=record];\n" +
+          @nodes.map { |node|
+            label = "<f0>#{node.name}"
+
+            node.fields.each_with_index do |field, i|
+              label += "|<f#{i + 1}>#{quote field}"
+            end
+
+            "#{node.id} [label=\"#{label}\"];"
+          }.join("\n") + "\n" + @edges.map { |edge|
+            "#{edge.from.id} -> #{edge.to.id} [label=\"#{edge.name}\"];"
+          }.join("\n") + "\n}"
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/ibm_db.rb b/activerecord/lib/arel/visitors/ibm_db.rb
new file mode 100644
index 0000000000..e85a5a08a7
--- /dev/null
+++ b/activerecord/lib/arel/visitors/ibm_db.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class IBM_DB < Arel::Visitors::ToSql
+      private
+
+      def visit_Arel_Nodes_Limit o, collector
+        collector << "FETCH FIRST "
+        collector = visit o.expr, collector
+        collector << " ROWS ONLY"
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/informix.rb b/activerecord/lib/arel/visitors/informix.rb
new file mode 100644
index 0000000000..44b18b550e
--- /dev/null
+++ b/activerecord/lib/arel/visitors/informix.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class Informix < Arel::Visitors::ToSql
+      private
+      def visit_Arel_Nodes_SelectStatement o, collector
+        collector << "SELECT "
+        collector = maybe_visit o.offset, collector
+        collector = maybe_visit o.limit, collector
+        collector = o.cores.inject(collector) { |c,x|
+          visit_Arel_Nodes_SelectCore x, c
+        }
+        if o.orders.any?
+          collector << "ORDER BY "
+          collector = inject_join o.orders, collector, ", "
+        end
+        collector = maybe_visit o.lock, collector
+      end
+      def visit_Arel_Nodes_SelectCore o, collector
+        collector = inject_join o.projections, collector, ", "
+        if o.source && !o.source.empty?
+          collector << " FROM "
+          collector = visit o.source, collector
+        end
+
+        if o.wheres.any?
+          collector << " WHERE "
+          collector = inject_join o.wheres, collector, " AND "
+        end
+
+        if o.groups.any?
+          collector << "GROUP BY "
+          collector = inject_join o.groups, collector, ", "
+        end
+
+        if o.havings.any?
+          collector << " HAVING "
+          collector = inject_join o.havings, collector, " AND "
+        end
+        collector
+      end
+
+      def visit_Arel_Nodes_Offset o, collector
+        collector << "SKIP "
+        visit o.expr, collector
+      end
+      def visit_Arel_Nodes_Limit o, collector
+        collector << "FIRST "
+        visit o.expr, collector
+        collector << " "
+      end
+    end
+  end
+end
+
diff --git a/activerecord/lib/arel/visitors/mssql.rb b/activerecord/lib/arel/visitors/mssql.rb
new file mode 100644
index 0000000000..8347d05d06
--- /dev/null
+++ b/activerecord/lib/arel/visitors/mssql.rb
@@ -0,0 +1,124 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class MSSQL < Arel::Visitors::ToSql
+      RowNumber = Struct.new :children
+
+      def initialize(*)
+        @primary_keys = {}
+        super
+      end
+
+      private
+
+      # `top` wouldn't really work here. I.e. User.select("distinct first_name").limit(10) would generate
+      # "select top 10 distinct first_name from users", which is invalid query! it should be
+      # "select distinct top 10 first_name from users"
+      def visit_Arel_Nodes_Top o
+        ""
+      end
+
+      def visit_Arel_Visitors_MSSQL_RowNumber o, collector
+        collector << "ROW_NUMBER() OVER (ORDER BY "
+        inject_join(o.children, collector, ', ') << ") as _row_num"
+      end
+
+      def visit_Arel_Nodes_SelectStatement o, collector
+        if !o.limit && !o.offset
+          return super
+        end
+
+        is_select_count = false
+        o.cores.each { |x|
+          core_order_by = row_num_literal determine_order_by(o.orders, x)
+          if select_count? x
+            x.projections = [core_order_by]
+            is_select_count = true
+          else
+            x.projections << core_order_by
+          end
+        }
+
+        if is_select_count
+          # fixme count distinct wouldn't work with limit or offset
+          collector << "SELECT COUNT(1) as count_id FROM ("
+        end
+
+        collector << "SELECT _t.* FROM ("
+        collector = o.cores.inject(collector) { |c,x|
+          visit_Arel_Nodes_SelectCore x, c
+        }
+        collector << ") as _t WHERE #{get_offset_limit_clause(o)}"
+
+        if is_select_count
+          collector << ") AS subquery"
+        else
+          collector
+        end
+      end
+
+      def get_offset_limit_clause o
+        first_row = o.offset ? o.offset.expr.to_i + 1 : 1
+        last_row  = o.limit ? o.limit.expr.to_i - 1 + first_row : nil
+        if last_row
+          " _row_num BETWEEN #{first_row} AND #{last_row}"
+        else
+          " _row_num >= #{first_row}"
+        end
+      end
+
+      def visit_Arel_Nodes_DeleteStatement o, collector
+        collector << 'DELETE '
+        if o.limit
+          collector << 'TOP ('
+          visit o.limit.expr, collector
+          collector << ') '
+        end
+        collector << 'FROM '
+        collector = visit o.relation, collector
+        if o.wheres.any?
+          collector << ' WHERE '
+          inject_join o.wheres, collector, AND
+        else
+          collector
+        end
+      end
+
+      def determine_order_by orders, x
+        if orders.any?
+          orders
+        elsif x.groups.any?
+          x.groups
+        else
+          pk = find_left_table_pk(x.froms)
+          pk ? [pk] : []
+        end
+      end
+
+      def row_num_literal order_by
+        RowNumber.new order_by
+      end
+
+      def select_count? x
+        x.projections.length == 1 && Arel::Nodes::Count === x.projections.first
+      end
+
+      # FIXME raise exception of there is no pk?
+      def find_left_table_pk o
+        if o.kind_of?(Arel::Nodes::Join)
+          find_left_table_pk(o.left)
+        elsif o.instance_of?(Arel::Table)
+          find_primary_key(o)
+        end
+      end
+
+      def find_primary_key(o)
+        @primary_keys[o.name] ||= begin
+          primary_key_name = @connection.primary_key(o.name)
+          # some tables might be without primary key
+          primary_key_name && o[primary_key_name]
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/mysql.rb b/activerecord/lib/arel/visitors/mysql.rb
new file mode 100644
index 0000000000..4c734f6292
--- /dev/null
+++ b/activerecord/lib/arel/visitors/mysql.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class MySQL < Arel::Visitors::ToSql
+      private
+      def visit_Arel_Nodes_Union o, collector, suppress_parens = false
+        unless suppress_parens
+          collector << "( "
+        end
+
+        collector =   case o.left
+                      when Arel::Nodes::Union
+                        visit_Arel_Nodes_Union o.left, collector, true
+                      else
+                        visit o.left, collector
+                      end
+
+        collector << " UNION "
+
+        collector =    case o.right
+                       when Arel::Nodes::Union
+                         visit_Arel_Nodes_Union o.right, collector, true
+                       else
+                         visit o.right, collector
+                       end
+
+        if suppress_parens
+          collector
+        else
+          collector << " )"
+        end
+      end
+
+      def visit_Arel_Nodes_Bin o, collector
+        collector << "BINARY "
+        visit o.expr, collector
+      end
+
+      ###
+      # :'(
+      # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
+      def visit_Arel_Nodes_SelectStatement o, collector
+        if o.offset && !o.limit
+          o.limit = Arel::Nodes::Limit.new(18446744073709551615)
+        end
+        super
+      end
+
+      def visit_Arel_Nodes_SelectCore o, collector
+        o.froms ||= Arel.sql('DUAL')
+        super
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o, collector
+        collector << "UPDATE "
+        collector = visit o.relation, collector
+
+        unless o.values.empty?
+          collector << " SET "
+          collector = inject_join o.values, collector, ', '
+        end
+
+        unless o.wheres.empty?
+          collector << " WHERE "
+          collector = inject_join o.wheres, collector, ' AND '
+        end
+
+        unless o.orders.empty?
+          collector << " ORDER BY "
+          collector = inject_join o.orders, collector, ', '
+        end
+
+        maybe_visit o.limit, collector
+      end
+
+      def visit_Arel_Nodes_Concat o, collector
+        collector << " CONCAT("
+        visit o.left, collector
+        collector << ", "
+        visit o.right, collector
+        collector << ") "
+        collector
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/oracle.rb b/activerecord/lib/arel/visitors/oracle.rb
new file mode 100644
index 0000000000..d4749bbae3
--- /dev/null
+++ b/activerecord/lib/arel/visitors/oracle.rb
@@ -0,0 +1,153 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class Oracle < Arel::Visitors::ToSql
+      private
+
+      def visit_Arel_Nodes_SelectStatement o, collector
+        o = order_hacks(o)
+
+        # if need to select first records without ORDER BY and GROUP BY and without DISTINCT
+        # then can use simple ROWNUM in WHERE clause
+        if o.limit && o.orders.empty? && o.cores.first.groups.empty? && !o.offset && o.cores.first.set_quantifier.class.to_s !~ /Distinct/
+          o.cores.last.wheres.push Nodes::LessThanOrEqual.new(
+            Nodes::SqlLiteral.new('ROWNUM'), o.limit.expr
+          )
+          return super
+        end
+
+        if o.limit && o.offset
+          o        = o.dup
+          limit    = o.limit.expr
+          offset   = o.offset
+          o.offset = nil
+          collector << "
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM ("
+
+          collector = super(o, collector)
+
+          if offset.expr.is_a? Nodes::BindParam
+            collector << ') raw_sql_ WHERE rownum <= ('
+            collector = visit offset.expr, collector
+            collector << ' + '
+            collector = visit limit, collector
+            collector << ") ) WHERE raw_rnum_ > "
+            collector = visit offset.expr, collector
+            return collector
+          else
+            collector << ") raw_sql_
+                WHERE rownum <= #{offset.expr.to_i + limit}
+              )
+              WHERE "
+            return visit(offset, collector)
+          end
+        end
+
+        if o.limit
+          o       = o.dup
+          limit   = o.limit.expr
+          collector << "SELECT * FROM ("
+          collector = super(o, collector)
+          collector << ") WHERE ROWNUM <= "
+          return visit limit, collector
+        end
+
+        if o.offset
+          o        = o.dup
+          offset   = o.offset
+          o.offset = nil
+          collector << "SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM ("
+          collector = super(o, collector)
+          collector << ") raw_sql_
+              )
+              WHERE "
+          return visit offset, collector
+        end
+
+        super
+      end
+
+      def visit_Arel_Nodes_Limit o, collector
+        collector
+      end
+
+      def visit_Arel_Nodes_Offset o, collector
+        collector << "raw_rnum_ > "
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_Except o, collector
+        collector << "( "
+        collector = infix_value o, collector, " MINUS "
+        collector << " )"
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o, collector
+        # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
+        if o.orders.any? && o.limit.nil?
+          # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
+          # otherwise let the user deal with the error
+          o = o.dup
+          o.orders = []
+        end
+
+        super
+      end
+
+      ###
+      # Hacks for the order clauses specific to Oracle
+      def order_hacks o
+        return o if o.orders.empty?
+        return o unless o.cores.any? do |core|
+          core.projections.any? do |projection|
+            /FIRST_VALUE/ === projection
+          end
+        end
+        # Previous version with join and split broke ORDER BY clause
+        # if it contained functions with several arguments (separated by ',').
+        #
+        # orders   = o.orders.map { |x| visit x }.join(', ').split(',')
+        orders   = o.orders.map do |x|
+          string = visit(x, Arel::Collectors::SQLString.new).value
+          if string.include?(',')
+            split_order_string(string)
+          else
+            string
+          end
+        end.flatten
+        o.orders = []
+        orders.each_with_index do |order, i|
+          o.orders <<
+            Nodes::SqlLiteral.new("alias_#{i}__#{' DESC' if /\bdesc$/i === order}")
+        end
+        o
+      end
+
+      # Split string by commas but count opening and closing brackets
+      # and ignore commas inside brackets.
+      def split_order_string(string)
+        array = []
+        i = 0
+        string.split(',').each do |part|
+          if array[i]
+            array[i] << ',' << part
+          else
+            # to ensure that array[i] will be String and not Arel::Nodes::SqlLiteral
+            array[i] = part.to_s
+          end
+          i += 1 if array[i].count('(') == array[i].count(')')
+        end
+        array
+      end
+
+      def visit_Arel_Nodes_BindParam o, collector
+        collector.add_bind(o.value) { |i| ":a#{i}" }
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/oracle12.rb b/activerecord/lib/arel/visitors/oracle12.rb
new file mode 100644
index 0000000000..648047ae61
--- /dev/null
+++ b/activerecord/lib/arel/visitors/oracle12.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class Oracle12 < Arel::Visitors::ToSql
+      private
+
+      def visit_Arel_Nodes_SelectStatement o, collector
+        # Oracle does not allow LIMIT clause with select for update
+        if o.limit && o.lock
+          raise ArgumentError, <<-MSG
+            'Combination of limit and lock is not supported.
+            because generated SQL statements
+            `SELECT FOR UPDATE and FETCH FIRST n ROWS` generates ORA-02014.`
+          MSG
+        end
+        super
+      end
+
+      def visit_Arel_Nodes_SelectOptions o, collector
+        collector = maybe_visit o.offset, collector
+        collector = maybe_visit o.limit, collector
+        collector = maybe_visit o.lock, collector
+      end
+
+      def visit_Arel_Nodes_Limit o, collector
+        collector << "FETCH FIRST "
+        collector = visit o.expr, collector
+        collector << " ROWS ONLY"
+      end
+
+      def visit_Arel_Nodes_Offset o, collector
+        collector << "OFFSET "
+        visit o.expr, collector
+        collector << " ROWS"
+      end
+
+      def visit_Arel_Nodes_Except o, collector
+        collector << "( "
+        collector = infix_value o, collector, " MINUS "
+        collector << " )"
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o, collector
+        # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
+        if o.orders.any? && o.limit.nil?
+          # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
+          # otherwise let the user deal with the error
+          o = o.dup
+          o.orders = []
+        end
+
+        super
+      end
+
+      def visit_Arel_Nodes_BindParam o, collector
+        collector.add_bind(o.value) { |i| ":a#{i}" }
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/postgresql.rb b/activerecord/lib/arel/visitors/postgresql.rb
new file mode 100644
index 0000000000..047f71aaa6
--- /dev/null
+++ b/activerecord/lib/arel/visitors/postgresql.rb
@@ -0,0 +1,103 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class PostgreSQL < Arel::Visitors::ToSql
+      CUBE = 'CUBE'
+      ROLLUP = 'ROLLUP'
+      GROUPING_SET = 'GROUPING SET'
+      LATERAL = 'LATERAL'
+
+      private
+
+      def visit_Arel_Nodes_Matches o, collector
+        op = o.case_sensitive ? ' LIKE ' : ' ILIKE '
+        collector = infix_value o, collector, op
+        if o.escape
+          collector << ' ESCAPE '
+          visit o.escape, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_DoesNotMatch o, collector
+        op = o.case_sensitive ? ' NOT LIKE ' : ' NOT ILIKE '
+        collector = infix_value o, collector, op
+        if o.escape
+          collector << ' ESCAPE '
+          visit o.escape, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_Regexp o, collector
+        op = o.case_sensitive ? ' ~ ' : ' ~* '
+        infix_value o, collector, op
+      end
+
+      def visit_Arel_Nodes_NotRegexp o, collector
+        op = o.case_sensitive ? ' !~ ' : ' !~* '
+        infix_value o, collector, op
+      end
+
+      def visit_Arel_Nodes_DistinctOn o, collector
+        collector << "DISTINCT ON ( "
+        visit(o.expr, collector) << " )"
+      end
+
+      def visit_Arel_Nodes_BindParam o, collector
+        collector.add_bind(o.value) { |i| "$#{i}" }
+      end
+
+      def visit_Arel_Nodes_GroupingElement o, collector
+        collector << "( "
+        visit(o.expr, collector) << " )"
+      end
+
+      def visit_Arel_Nodes_Cube o, collector
+        collector << CUBE
+        grouping_array_or_grouping_element o, collector
+      end
+
+      def visit_Arel_Nodes_RollUp o, collector
+        collector << ROLLUP
+        grouping_array_or_grouping_element o, collector
+      end
+
+      def visit_Arel_Nodes_GroupingSet o, collector
+        collector << GROUPING_SET
+        grouping_array_or_grouping_element o, collector
+      end
+
+      def visit_Arel_Nodes_Lateral o, collector
+        collector << LATERAL
+        collector << SPACE
+        grouping_parentheses o, collector
+      end
+
+      # Used by Lateral visitor to enclose select queries in parentheses
+      def grouping_parentheses o, collector
+        if o.expr.is_a? Nodes::SelectStatement
+          collector << "("
+          visit o.expr, collector
+          collector << ")"
+        else
+          visit o.expr, collector
+        end
+      end
+
+      # Utilized by GroupingSet, Cube & RollUp visitors to
+      # handle grouping aggregation semantics
+      def grouping_array_or_grouping_element o, collector
+        if o.expr.is_a? Array
+          collector << "( "
+          visit o.expr, collector
+          collector << " )"
+        else
+          visit o.expr, collector
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/sqlite.rb b/activerecord/lib/arel/visitors/sqlite.rb
new file mode 100644
index 0000000000..4ae093968b
--- /dev/null
+++ b/activerecord/lib/arel/visitors/sqlite.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class SQLite < Arel::Visitors::ToSql
+      private
+
+      # Locks are not supported in SQLite
+      def visit_Arel_Nodes_Lock o, collector
+        collector
+      end
+
+      def visit_Arel_Nodes_SelectStatement o, collector
+        o.limit = Arel::Nodes::Limit.new(-1) if o.offset && !o.limit
+        super
+      end
+
+      def visit_Arel_Nodes_True o, collector
+        collector << "1"
+      end
+
+      def visit_Arel_Nodes_False o, collector
+        collector << "0"
+      end
+
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/to_sql.rb b/activerecord/lib/arel/visitors/to_sql.rb
new file mode 100644
index 0000000000..2b5c43b173
--- /dev/null
+++ b/activerecord/lib/arel/visitors/to_sql.rb
@@ -0,0 +1,846 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class UnsupportedVisitError < StandardError
+      def initialize(object)
+        super "Unsupported argument type: #{object.class.name}. Construct an Arel node instead."
+      end
+    end
+
+    class ToSql < Arel::Visitors::Visitor
+      ##
+      # This is some roflscale crazy stuff.  I'm roflscaling this because
+      # building SQL queries is a hotspot.  I will explain the roflscale so that
+      # others will not rm this code.
+      #
+      # In YARV, string literals in a method body will get duped when the byte
+      # code is executed.  Let's take a look:
+      #
+      # > puts RubyVM::InstructionSequence.new('def foo; "bar"; end').disasm
+      #
+      #   == disasm: <RubyVM::InstructionSequence:foo@<compiled>>=====
+      #    0000 trace            8
+      #    0002 trace            1
+      #    0004 putstring        "bar"
+      #    0006 trace            16
+      #    0008 leave
+      #
+      # The `putstring` bytecode will dup the string and push it on the stack.
+      # In many cases in our SQL visitor, that string is never mutated, so there
+      # is no need to dup the literal.
+      #
+      # If we change to a constant lookup, the string will not be duped, and we
+      # can reduce the objects in our system:
+      #
+      # > puts RubyVM::InstructionSequence.new('BAR = "bar"; def foo; BAR; end').disasm
+      #
+      #  == disasm: <RubyVM::InstructionSequence:foo@<compiled>>========
+      #  0000 trace            8
+      #  0002 trace            1
+      #  0004 getinlinecache   11, <ic:0>
+      #  0007 getconstant      :BAR
+      #  0009 setinlinecache   <ic:0>
+      #  0011 trace            16
+      #  0013 leave
+      #
+      # `getconstant` should be a hash lookup, and no object is duped when the
+      # value of the constant is pushed on the stack.  Hence the crazy
+      # constants below.
+      #
+      # `matches` and `doesNotMatch` operate case-insensitively via Visitor subclasses
+      # specialized for specific databases when necessary.
+      #
+
+      WHERE    = ' WHERE '    # :nodoc:
+      SPACE    = ' '          # :nodoc:
+      COMMA    = ', '         # :nodoc:
+      GROUP_BY = ' GROUP BY ' # :nodoc:
+      ORDER_BY = ' ORDER BY ' # :nodoc:
+      WINDOW   = ' WINDOW '   # :nodoc:
+      AND      = ' AND '      # :nodoc:
+
+      DISTINCT = 'DISTINCT'   # :nodoc:
+
+      def initialize connection
+        super()
+        @connection     = connection
+      end
+
+      def compile node, &block
+        accept(node, Arel::Collectors::SQLString.new, &block).value
+      end
+
+      private
+
+      def visit_Arel_Nodes_DeleteStatement o, collector
+        collector << 'DELETE FROM '
+        collector = visit o.relation, collector
+        if o.wheres.any?
+          collector << WHERE
+          collector = inject_join o.wheres, collector, AND
+        end
+
+        maybe_visit o.limit, collector
+      end
+
+      # FIXME: we should probably have a 2-pass visitor for this
+      def build_subselect key, o
+        stmt             = Nodes::SelectStatement.new
+        core             = stmt.cores.first
+        core.froms       = o.relation
+        core.wheres      = o.wheres
+        core.projections = [key]
+        stmt.limit       = o.limit
+        stmt.orders      = o.orders
+        stmt
+      end
+
+      def visit_Arel_Nodes_UpdateStatement o, collector
+        if o.orders.empty? && o.limit.nil?
+          wheres = o.wheres
+        else
+          wheres = [Nodes::In.new(o.key, [build_subselect(o.key, o)])]
+        end
+
+        collector << "UPDATE "
+        collector = visit o.relation, collector
+        unless o.values.empty?
+          collector << " SET "
+          collector = inject_join o.values, collector, ", "
+        end
+
+        unless wheres.empty?
+          collector << " WHERE "
+          collector = inject_join wheres, collector, " AND "
+        end
+
+        collector
+      end
+
+      def visit_Arel_Nodes_InsertStatement o, collector
+        collector << "INSERT INTO "
+        collector = visit o.relation, collector
+        if o.columns.any?
+          collector << " (#{o.columns.map { |x|
+            quote_column_name x.name
+          }.join ', '})"
+        end
+
+        if o.values
+          maybe_visit o.values, collector
+        elsif o.select
+          maybe_visit o.select, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_Exists o, collector
+        collector << "EXISTS ("
+        collector = visit(o.expressions, collector) << ")"
+        if o.alias
+          collector << " AS "
+          visit o.alias, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_Casted o, collector
+        collector << quoted(o.val, o.attribute).to_s
+      end
+
+      def visit_Arel_Nodes_Quoted o, collector
+        collector << quoted(o.expr, nil).to_s
+      end
+
+      def visit_Arel_Nodes_True o, collector
+        collector << "TRUE"
+      end
+
+      def visit_Arel_Nodes_False o, collector
+        collector << "FALSE"
+      end
+
+      def visit_Arel_Nodes_ValuesList o, collector
+        collector << "VALUES "
+
+        len = o.rows.length - 1
+        o.rows.each_with_index { |row, i|
+          collector << '('
+          row_len = row.length - 1
+          row.each_with_index do |value, k|
+            case value
+            when Nodes::SqlLiteral, Nodes::BindParam
+              collector = visit(value, collector)
+            else
+              collector << quote(value)
+            end
+            collector << COMMA unless k == row_len
+          end
+          collector << ')'
+          collector << COMMA unless i == len
+        }
+        collector
+      end
+
+      def visit_Arel_Nodes_Values o, collector
+        collector << "VALUES ("
+
+        len = o.expressions.length - 1
+        o.expressions.each_with_index { |value, i|
+          case value
+          when Nodes::SqlLiteral, Nodes::BindParam
+            collector = visit value, collector
+          else
+            collector << quote(value).to_s
+          end
+          unless i == len
+            collector << COMMA
+          end
+        }
+
+        collector << ")"
+      end
+
+      def visit_Arel_Nodes_SelectStatement o, collector
+        if o.with
+          collector = visit o.with, collector
+          collector << SPACE
+        end
+
+        collector = o.cores.inject(collector) { |c,x|
+          visit_Arel_Nodes_SelectCore(x, c)
+        }
+
+        unless o.orders.empty?
+          collector << ORDER_BY
+          len = o.orders.length - 1
+          o.orders.each_with_index { |x, i|
+            collector = visit(x, collector)
+            collector << COMMA unless len == i
+          }
+        end
+
+        visit_Arel_Nodes_SelectOptions(o, collector)
+
+        collector
+      end
+
+      def visit_Arel_Nodes_SelectOptions o, collector
+        collector = maybe_visit o.limit, collector
+        collector = maybe_visit o.offset, collector
+        collector = maybe_visit o.lock, collector
+      end
+
+      def visit_Arel_Nodes_SelectCore o, collector
+        collector << "SELECT"
+
+        collector = maybe_visit o.top, collector
+
+        collector = maybe_visit o.set_quantifier, collector
+
+        collect_nodes_for o.projections, collector, SPACE
+
+        if o.source && !o.source.empty?
+          collector << " FROM "
+          collector = visit o.source, collector
+        end
+
+        collect_nodes_for o.wheres, collector, WHERE, AND
+        collect_nodes_for o.groups, collector, GROUP_BY
+        unless o.havings.empty?
+          collector << " HAVING "
+          inject_join o.havings, collector, AND
+        end
+        collect_nodes_for o.windows, collector, WINDOW
+
+        collector
+      end
+
+      def collect_nodes_for nodes, collector, spacer, connector = COMMA
+        unless nodes.empty?
+          collector << spacer
+          len = nodes.length - 1
+          nodes.each_with_index do |x, i|
+            collector = visit(x, collector)
+            collector << connector unless len == i
+          end
+        end
+      end
+
+      def visit_Arel_Nodes_Bin o, collector
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_Distinct o, collector
+        collector << DISTINCT
+      end
+
+      def visit_Arel_Nodes_DistinctOn o, collector
+        raise NotImplementedError, 'DISTINCT ON not implemented for this db'
+      end
+
+      def visit_Arel_Nodes_With o, collector
+        collector << "WITH "
+        inject_join o.children, collector, COMMA
+      end
+
+      def visit_Arel_Nodes_WithRecursive o, collector
+        collector << "WITH RECURSIVE "
+        inject_join o.children, collector, COMMA
+      end
+
+      def visit_Arel_Nodes_Union o, collector
+        collector << "( "
+        infix_value(o, collector, " UNION ") << " )"
+      end
+
+      def visit_Arel_Nodes_UnionAll o, collector
+        collector << "( "
+        infix_value(o, collector, " UNION ALL ") << " )"
+      end
+
+      def visit_Arel_Nodes_Intersect o, collector
+        collector << "( "
+        infix_value(o, collector, " INTERSECT ") << " )"
+      end
+
+      def visit_Arel_Nodes_Except o, collector
+        collector << "( "
+        infix_value(o, collector, " EXCEPT ") << " )"
+      end
+
+      def visit_Arel_Nodes_NamedWindow o, collector
+        collector << quote_column_name(o.name)
+        collector << " AS "
+        visit_Arel_Nodes_Window o, collector
+      end
+
+      def visit_Arel_Nodes_Window o, collector
+        collector << "("
+
+        if o.partitions.any?
+          collector << "PARTITION BY "
+          collector = inject_join o.partitions, collector, ", "
+        end
+
+        if o.orders.any?
+          collector << SPACE if o.partitions.any?
+          collector << "ORDER BY "
+          collector = inject_join o.orders, collector, ", "
+        end
+
+        if o.framing
+          collector << SPACE if o.partitions.any? or o.orders.any?
+          collector = visit o.framing, collector
+        end
+
+        collector << ")"
+      end
+
+      def visit_Arel_Nodes_Rows o, collector
+        if o.expr
+          collector << "ROWS "
+          visit o.expr, collector
+        else
+          collector << "ROWS"
+        end
+      end
+
+      def visit_Arel_Nodes_Range o, collector
+        if o.expr
+          collector << "RANGE "
+          visit o.expr, collector
+        else
+          collector << "RANGE"
+        end
+      end
+
+      def visit_Arel_Nodes_Preceding o, collector
+        collector = if o.expr
+                      visit o.expr, collector
+                    else
+                      collector << "UNBOUNDED"
+                    end
+
+        collector << " PRECEDING"
+      end
+
+      def visit_Arel_Nodes_Following o, collector
+        collector = if o.expr
+                      visit o.expr, collector
+                    else
+                      collector << "UNBOUNDED"
+                    end
+
+        collector << " FOLLOWING"
+      end
+
+      def visit_Arel_Nodes_CurrentRow o, collector
+        collector << "CURRENT ROW"
+      end
+
+      def visit_Arel_Nodes_Over o, collector
+        case o.right
+        when nil
+          visit(o.left, collector) << " OVER ()"
+        when Arel::Nodes::SqlLiteral
+          infix_value o, collector, " OVER "
+        when String, Symbol
+          visit(o.left, collector) << " OVER #{quote_column_name o.right.to_s}"
+        else
+          infix_value o, collector, " OVER "
+        end
+      end
+
+      def visit_Arel_Nodes_Offset o, collector
+        collector << "OFFSET "
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_Limit o, collector
+        collector << "LIMIT "
+        visit o.expr, collector
+      end
+
+      # FIXME: this does nothing on most databases, but does on MSSQL
+      def visit_Arel_Nodes_Top o, collector
+        collector
+      end
+
+      def visit_Arel_Nodes_Lock o, collector
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_Grouping o, collector
+        if o.expr.is_a? Nodes::Grouping
+          visit(o.expr, collector)
+        else
+          collector << "("
+          visit(o.expr, collector) << ")"
+        end
+      end
+
+      def visit_Arel_SelectManager o, collector
+        collector << '('
+        visit(o.ast, collector) << ')'
+      end
+
+      def visit_Arel_Nodes_Ascending o, collector
+        visit(o.expr, collector) << " ASC"
+      end
+
+      def visit_Arel_Nodes_Descending o, collector
+        visit(o.expr, collector) << " DESC"
+      end
+
+      def visit_Arel_Nodes_Group o, collector
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_NamedFunction o, collector
+        collector << o.name
+        collector << "("
+        collector << "DISTINCT " if o.distinct
+        collector = inject_join(o.expressions, collector, ", ") << ")"
+        if o.alias
+          collector << " AS "
+          visit o.alias, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_Extract o, collector
+        collector << "EXTRACT(#{o.field.to_s.upcase} FROM "
+        visit(o.expr, collector) << ")"
+      end
+
+      def visit_Arel_Nodes_Count o, collector
+        aggregate "COUNT", o, collector
+      end
+
+      def visit_Arel_Nodes_Sum o, collector
+        aggregate "SUM", o, collector
+      end
+
+      def visit_Arel_Nodes_Max o, collector
+        aggregate "MAX", o, collector
+      end
+
+      def visit_Arel_Nodes_Min o, collector
+        aggregate "MIN", o, collector
+      end
+
+      def visit_Arel_Nodes_Avg o, collector
+        aggregate "AVG", o, collector
+      end
+
+      def visit_Arel_Nodes_TableAlias o, collector
+        collector = visit o.relation, collector
+        collector << " "
+        collector << quote_table_name(o.name)
+      end
+
+      def visit_Arel_Nodes_Between o, collector
+        collector = visit o.left, collector
+        collector << " BETWEEN "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_GreaterThanOrEqual o, collector
+        collector = visit o.left, collector
+        collector << " >= "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_GreaterThan o, collector
+        collector = visit o.left, collector
+        collector << " > "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_LessThanOrEqual o, collector
+        collector = visit o.left, collector
+        collector << " <= "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_LessThan o, collector
+        collector = visit o.left, collector
+        collector << " < "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_Matches o, collector
+        collector = visit o.left, collector
+        collector << " LIKE "
+        collector = visit o.right, collector
+        if o.escape
+          collector << ' ESCAPE '
+          visit o.escape, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_DoesNotMatch o, collector
+        collector = visit o.left, collector
+        collector << " NOT LIKE "
+        collector = visit o.right, collector
+        if o.escape
+          collector << ' ESCAPE '
+          visit o.escape, collector
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_JoinSource o, collector
+        if o.left
+          collector = visit o.left, collector
+        end
+        if o.right.any?
+          collector << SPACE if o.left
+          collector = inject_join o.right, collector, SPACE
+        end
+        collector
+      end
+
+      def visit_Arel_Nodes_Regexp o, collector
+        raise NotImplementedError, '~ not implemented for this db'
+      end
+
+      def visit_Arel_Nodes_NotRegexp o, collector
+        raise NotImplementedError, '!~ not implemented for this db'
+      end
+
+      def visit_Arel_Nodes_StringJoin o, collector
+        visit o.left, collector
+      end
+
+      def visit_Arel_Nodes_FullOuterJoin o, collector
+        collector << "FULL OUTER JOIN "
+        collector = visit o.left, collector
+        collector << SPACE
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_OuterJoin o, collector
+        collector << "LEFT OUTER JOIN "
+        collector = visit o.left, collector
+        collector << " "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_RightOuterJoin o, collector
+        collector << "RIGHT OUTER JOIN "
+        collector = visit o.left, collector
+        collector << SPACE
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_InnerJoin o, collector
+        collector << "INNER JOIN "
+        collector = visit o.left, collector
+        if o.right
+          collector << SPACE
+          visit(o.right, collector)
+        else
+          collector
+        end
+      end
+
+      def visit_Arel_Nodes_On o, collector
+        collector << "ON "
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_Not o, collector
+        collector << "NOT ("
+        visit(o.expr, collector) << ")"
+      end
+
+      def visit_Arel_Table o, collector
+        if o.table_alias
+          collector << "#{quote_table_name o.name} #{quote_table_name o.table_alias}"
+        else
+          collector << quote_table_name(o.name)
+        end
+      end
+
+      def visit_Arel_Nodes_In o, collector
+        if Array === o.right && o.right.empty?
+          collector << '1=0'
+        else
+          collector = visit o.left, collector
+          collector << " IN ("
+          visit(o.right, collector) << ")"
+        end
+      end
+
+      def visit_Arel_Nodes_NotIn o, collector
+        if Array === o.right && o.right.empty?
+          collector << '1=1'
+        else
+          collector = visit o.left, collector
+          collector << " NOT IN ("
+          collector = visit o.right, collector
+          collector << ")"
+        end
+      end
+
+      def visit_Arel_Nodes_And o, collector
+        inject_join o.children, collector, " AND "
+      end
+
+      def visit_Arel_Nodes_Or o, collector
+        collector = visit o.left, collector
+        collector << " OR "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_Assignment o, collector
+        case o.right
+        when Arel::Nodes::UnqualifiedColumn, Arel::Attributes::Attribute, Arel::Nodes::BindParam
+          collector = visit o.left, collector
+          collector << " = "
+          visit o.right, collector
+        else
+          collector = visit o.left, collector
+          collector << " = "
+          collector << quote(o.right).to_s
+        end
+      end
+
+      def visit_Arel_Nodes_Equality o, collector
+        right = o.right
+
+        collector = visit o.left, collector
+
+        if right.nil?
+          collector << " IS NULL"
+        else
+          collector << " = "
+          visit right, collector
+        end
+      end
+
+      def visit_Arel_Nodes_NotEqual o, collector
+        right = o.right
+
+        collector = visit o.left, collector
+
+        if right.nil?
+          collector << " IS NOT NULL"
+        else
+          collector << " != "
+          visit right, collector
+        end
+      end
+
+      def visit_Arel_Nodes_As o, collector
+        collector = visit o.left, collector
+        collector << " AS "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_Case o, collector
+        collector << "CASE "
+        if o.case
+          visit o.case, collector
+          collector << " "
+        end
+        o.conditions.each do |condition|
+          visit condition, collector
+          collector << " "
+        end
+        if o.default
+          visit o.default, collector
+          collector << " "
+        end
+        collector << "END"
+      end
+
+      def visit_Arel_Nodes_When o, collector
+        collector << "WHEN "
+        visit o.left, collector
+        collector << " THEN "
+        visit o.right, collector
+      end
+
+      def visit_Arel_Nodes_Else o, collector
+        collector << "ELSE "
+        visit o.expr, collector
+      end
+
+      def visit_Arel_Nodes_UnqualifiedColumn o, collector
+        collector << "#{quote_column_name o.name}"
+        collector
+      end
+
+      def visit_Arel_Attributes_Attribute o, collector
+        join_name = o.relation.table_alias || o.relation.name
+        collector << "#{quote_table_name join_name}.#{quote_column_name o.name}"
+      end
+      alias :visit_Arel_Attributes_Integer :visit_Arel_Attributes_Attribute
+      alias :visit_Arel_Attributes_Float :visit_Arel_Attributes_Attribute
+      alias :visit_Arel_Attributes_Decimal :visit_Arel_Attributes_Attribute
+      alias :visit_Arel_Attributes_String :visit_Arel_Attributes_Attribute
+      alias :visit_Arel_Attributes_Time :visit_Arel_Attributes_Attribute
+      alias :visit_Arel_Attributes_Boolean :visit_Arel_Attributes_Attribute
+
+      def literal o, collector; collector << o.to_s; end
+
+      def visit_Arel_Nodes_BindParam o, collector
+        collector.add_bind(o.value) { "?" }
+      end
+
+      alias :visit_Arel_Nodes_SqlLiteral :literal
+      alias :visit_Bignum                :literal
+      alias :visit_Fixnum                :literal
+      alias :visit_Integer               :literal
+
+      def quoted o, a
+        if a && a.able_to_type_cast?
+          quote(a.type_cast_for_database(o))
+        else
+          quote(o)
+        end
+      end
+
+      def unsupported o, collector
+        raise UnsupportedVisitError.new(o)
+      end
+
+      alias :visit_ActiveSupport_Multibyte_Chars :unsupported
+      alias :visit_ActiveSupport_StringInquirer  :unsupported
+      alias :visit_BigDecimal                    :unsupported
+      alias :visit_Class                         :unsupported
+      alias :visit_Date                          :unsupported
+      alias :visit_DateTime                      :unsupported
+      alias :visit_FalseClass                    :unsupported
+      alias :visit_Float                         :unsupported
+      alias :visit_Hash                          :unsupported
+      alias :visit_NilClass                      :unsupported
+      alias :visit_String                        :unsupported
+      alias :visit_Symbol                        :unsupported
+      alias :visit_Time                          :unsupported
+      alias :visit_TrueClass                     :unsupported
+
+      def visit_Arel_Nodes_InfixOperation o, collector
+        collector = visit o.left, collector
+        collector << " #{o.operator} "
+        visit o.right, collector
+      end
+
+      alias :visit_Arel_Nodes_Addition       :visit_Arel_Nodes_InfixOperation
+      alias :visit_Arel_Nodes_Subtraction    :visit_Arel_Nodes_InfixOperation
+      alias :visit_Arel_Nodes_Multiplication :visit_Arel_Nodes_InfixOperation
+      alias :visit_Arel_Nodes_Division       :visit_Arel_Nodes_InfixOperation
+
+      def visit_Arel_Nodes_UnaryOperation o, collector
+        collector << " #{o.operator} "
+        visit o.expr, collector
+      end
+
+      def visit_Array o, collector
+        inject_join o, collector, ", "
+      end
+      alias :visit_Set :visit_Array
+
+      def quote value
+        return value if Arel::Nodes::SqlLiteral === value
+        @connection.quote value
+      end
+
+      def quote_table_name name
+        return name if Arel::Nodes::SqlLiteral === name
+        @connection.quote_table_name(name)
+      end
+
+      def quote_column_name name
+        return name if Arel::Nodes::SqlLiteral === name
+        @connection.quote_column_name(name)
+      end
+
+      def maybe_visit thing, collector
+        return collector unless thing
+        collector << " "
+        visit thing, collector
+      end
+
+      def inject_join list, collector, join_str
+        len = list.length - 1
+        list.each_with_index.inject(collector) { |c, (x,i)|
+          if i == len
+            visit x, c
+          else
+            visit(x, c) << join_str
+          end
+        }
+      end
+
+      def infix_value o, collector, value
+        collector = visit o.left, collector
+        collector << value
+        visit o.right, collector
+      end
+
+      def aggregate name, o, collector
+        collector << "#{name}("
+        if o.distinct
+          collector << "DISTINCT "
+        end
+        collector = inject_join(o.expressions, collector, ", ") << ")"
+        if o.alias
+          collector << " AS "
+          visit o.alias, collector
+        else
+          collector
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/visitor.rb b/activerecord/lib/arel/visitors/visitor.rb
new file mode 100644
index 0000000000..f156be9a0a
--- /dev/null
+++ b/activerecord/lib/arel/visitors/visitor.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class Visitor
+      def initialize
+        @dispatch = get_dispatch_cache
+      end
+
+      def accept object, *args
+        visit object, *args
+      end
+
+      private
+
+      attr_reader :dispatch
+
+      def self.dispatch_cache
+        Hash.new do |hash, klass|
+          hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
+        end
+      end
+
+      def get_dispatch_cache
+        self.class.dispatch_cache
+      end
+
+      def visit object, *args
+        dispatch_method = dispatch[object.class]
+        send dispatch_method, object, *args
+      rescue NoMethodError => e
+        raise e if respond_to?(dispatch_method, true)
+        superklass = object.class.ancestors.find { |klass|
+          respond_to?(dispatch[klass], true)
+        }
+        raise(TypeError, "Cannot visit #{object.class}") unless superklass
+        dispatch[object.class] = dispatch[superklass]
+        retry
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/where_sql.rb b/activerecord/lib/arel/visitors/where_sql.rb
new file mode 100644
index 0000000000..55e6ca9a21
--- /dev/null
+++ b/activerecord/lib/arel/visitors/where_sql.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+module Arel
+  module Visitors
+    class WhereSql < Arel::Visitors::ToSql
+      def initialize(inner_visitor, *args, &block)
+        @inner_visitor = inner_visitor
+        super(*args, &block)
+      end
+
+      private
+
+      def visit_Arel_Nodes_SelectCore o, collector
+        collector << "WHERE "
+        wheres = o.wheres.map do |where|
+          Nodes::SqlLiteral.new(@inner_visitor.accept(where, collector.class.new).value)
+        end
+
+        inject_join wheres, collector, ' AND '
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/window_predications.rb b/activerecord/lib/arel/window_predications.rb
new file mode 100644
index 0000000000..f93dede036
--- /dev/null
+++ b/activerecord/lib/arel/window_predications.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+module Arel
+  module WindowPredications
+
+    def over(expr = nil)
+      Nodes::Over.new(self, expr)
+    end
+
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/cases/arel/attributes/attribute_test.rb b/activerecord/test/cases/arel/attributes/attribute_test.rb
new file mode 100644
index 0000000000..802d6e743f
--- /dev/null
+++ b/activerecord/test/cases/arel/attributes/attribute_test.rb
@@ -0,0 +1,1014 @@
+# frozen_string_literal: true
+require_relative '../helper'
+require 'ostruct'
+
+module Arel
+  module Attributes
+    class AttributeTest < Arel::Spec
+      describe '#not_eq' do
+        it 'should create a NotEqual node' do
+          relation = Table.new(:users)
+          relation[:id].not_eq(10).must_be_kind_of Nodes::NotEqual
+        end
+
+        it 'should generate != in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" != 10
+          }
+        end
+
+        it 'should handle nil' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq(nil)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IS NOT NULL
+          }
+        end
+      end
+
+      describe '#not_eq_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].not_eq_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" != 1 OR "users"."id" != 2)
+          }
+        end
+      end
+
+      describe '#not_eq_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].not_eq_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" != 1 AND "users"."id" != 2)
+          }
+        end
+      end
+
+      describe '#gt' do
+        it 'should create a GreaterThan node' do
+          relation = Table.new(:users)
+          relation[:id].gt(10).must_be_kind_of Nodes::GreaterThan
+        end
+
+        it 'should generate > in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" > 10
+          }
+        end
+
+        it 'should handle comparing with a subquery' do
+          users = Table.new(:users)
+
+          avg = users.project(users[:karma].average)
+          mgr = users.project(Arel.star).where(users[:karma].gt(avg))
+
+          mgr.to_sql.must_be_like %{
+            SELECT * FROM "users" WHERE "users"."karma" > (SELECT AVG("users"."karma") FROM "users")
+          }
+        end
+
+        it 'should accept various data types.' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].gt('fake_name')
+          mgr.to_sql.must_match %{"users"."name" > 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].gt(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" > '#{current_time}'}
+        end
+      end
+
+      describe '#gt_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].gt_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" > 1 OR "users"."id" > 2)
+          }
+        end
+      end
+
+      describe '#gt_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].gt_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" > 1 AND "users"."id" > 2)
+          }
+        end
+      end
+
+      describe '#gteq' do
+        it 'should create a GreaterThanOrEqual node' do
+          relation = Table.new(:users)
+          relation[:id].gteq(10).must_be_kind_of Nodes::GreaterThanOrEqual
+        end
+
+        it 'should generate >= in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" >= 10
+          }
+        end
+
+        it 'should accept various data types.' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].gteq('fake_name')
+          mgr.to_sql.must_match %{"users"."name" >= 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].gteq(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" >= '#{current_time}'}
+        end
+      end
+
+      describe '#gteq_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].gteq_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" >= 1 OR "users"."id" >= 2)
+          }
+        end
+      end
+
+      describe '#gteq_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].gteq_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" >= 1 AND "users"."id" >= 2)
+          }
+        end
+      end
+
+      describe '#lt' do
+        it 'should create a LessThan node' do
+          relation = Table.new(:users)
+          relation[:id].lt(10).must_be_kind_of Nodes::LessThan
+        end
+
+        it 'should generate < in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" < 10
+          }
+        end
+
+        it 'should accept various data types.' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].lt('fake_name')
+          mgr.to_sql.must_match %{"users"."name" < 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].lt(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" < '#{current_time}'}
+        end
+      end
+
+      describe '#lt_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].lt_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" < 1 OR "users"."id" < 2)
+          }
+        end
+      end
+
+      describe '#lt_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].lt_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" < 1 AND "users"."id" < 2)
+          }
+        end
+      end
+
+      describe '#lteq' do
+        it 'should create a LessThanOrEqual node' do
+          relation = Table.new(:users)
+          relation[:id].lteq(10).must_be_kind_of Nodes::LessThanOrEqual
+        end
+
+        it 'should generate <= in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" <= 10
+          }
+        end
+
+        it 'should accept various data types.' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].lteq('fake_name')
+          mgr.to_sql.must_match %{"users"."name" <= 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].lteq(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" <= '#{current_time}'}
+        end
+      end
+
+      describe '#lteq_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].lteq_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" <= 1 OR "users"."id" <= 2)
+          }
+        end
+      end
+
+      describe '#lteq_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].lteq_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" <= 1 AND "users"."id" <= 2)
+          }
+        end
+      end
+
+      describe '#average' do
+        it 'should create a AVG node' do
+          relation = Table.new(:users)
+          relation[:id].average.must_be_kind_of Nodes::Avg
+        end
+
+        it 'should generate the proper SQL' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].average
+          mgr.to_sql.must_be_like %{
+            SELECT AVG("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe '#maximum' do
+        it 'should create a MAX node' do
+          relation = Table.new(:users)
+          relation[:id].maximum.must_be_kind_of Nodes::Max
+        end
+
+        it 'should generate proper SQL' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].maximum
+          mgr.to_sql.must_be_like %{
+            SELECT MAX("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe '#minimum' do
+        it 'should create a Min node' do
+          relation = Table.new(:users)
+          relation[:id].minimum.must_be_kind_of Nodes::Min
+        end
+
+        it 'should generate proper SQL' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].minimum
+          mgr.to_sql.must_be_like %{
+            SELECT MIN("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe '#sum' do
+        it 'should create a SUM node' do
+          relation = Table.new(:users)
+          relation[:id].sum.must_be_kind_of Nodes::Sum
+        end
+
+        it 'should generate the proper SQL' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].sum
+          mgr.to_sql.must_be_like %{
+            SELECT SUM("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe '#count' do
+        it 'should return a count node' do
+          relation = Table.new(:users)
+          relation[:id].count.must_be_kind_of Nodes::Count
+        end
+
+        it 'should take a distinct param' do
+          relation = Table.new(:users)
+          count = relation[:id].count(nil)
+          count.must_be_kind_of Nodes::Count
+          count.distinct.must_be_nil
+        end
+      end
+
+      describe '#eq' do
+        it 'should return an equality node' do
+          attribute = Attribute.new nil, nil
+          equality = attribute.eq 1
+          equality.left.must_equal attribute
+          equality.right.val.must_equal 1
+          equality.must_be_kind_of Nodes::Equality
+        end
+
+        it 'should generate = in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" = 10
+          }
+        end
+
+        it 'should handle nil' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq(nil)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IS NULL
+          }
+        end
+      end
+
+      describe '#eq_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].eq_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_any([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 OR "users"."id" = 2)
+          }
+        end
+
+        it 'should not eat input' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          values = [1,2]
+          mgr.where relation[:id].eq_any(values)
+          values.must_equal [1,2]
+        end
+      end
+
+      describe '#eq_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].eq_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 AND "users"."id" = 2)
+          }
+        end
+
+        it 'should not eat input' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          values = [1,2]
+          mgr.where relation[:id].eq_all(values)
+          values.must_equal [1,2]
+        end
+      end
+
+      describe '#matches' do
+        it 'should create a Matches node' do
+          relation = Table.new(:users)
+          relation[:name].matches('%bacon%').must_be_kind_of Nodes::Matches
+        end
+
+        it 'should generate LIKE in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches('%bacon%')
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."name" LIKE '%bacon%'
+          }
+        end
+      end
+
+      describe '#matches_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:name].matches_any(['%chunky%','%bacon%']).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches_any(['%chunky%','%bacon%'])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" LIKE '%chunky%' OR "users"."name" LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe '#matches_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:name].matches_all(['%chunky%','%bacon%']).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches_all(['%chunky%','%bacon%'])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" LIKE '%chunky%' AND "users"."name" LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe '#does_not_match' do
+        it 'should create a DoesNotMatch node' do
+          relation = Table.new(:users)
+          relation[:name].does_not_match('%bacon%').must_be_kind_of Nodes::DoesNotMatch
+        end
+
+        it 'should generate NOT LIKE in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match('%bacon%')
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."name" NOT LIKE '%bacon%'
+          }
+        end
+      end
+
+      describe '#does_not_match_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:name].does_not_match_any(['%chunky%','%bacon%']).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_any(['%chunky%','%bacon%'])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" NOT LIKE '%chunky%' OR "users"."name" NOT LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe '#does_not_match_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:name].does_not_match_all(['%chunky%','%bacon%']).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(['%chunky%','%bacon%'])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" NOT LIKE '%chunky%' AND "users"."name" NOT LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe 'with a range' do
+        it 'can be constructed with a standard range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(1..3)
+
+          node.must_equal Nodes::Between.new(
+            attribute,
+            Nodes::And.new([
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(3, attribute)
+            ])
+          )
+        end
+
+        it 'can be constructed with a range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY..3)
+
+          node.must_equal Nodes::LessThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it 'can be constructed with a quoted range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, 3, false))
+
+          node.must_equal Nodes::LessThanOrEqual.new(
+            attribute,
+            Nodes::Quoted.new(3)
+          )
+        end
+
+        it 'can be constructed with an exclusive range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY...3)
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it 'can be constructed with a quoted exclusive range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, 3, true))
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Quoted.new(3)
+          )
+        end
+
+        it 'can be constructed with an infinite range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY..::Float::INFINITY)
+
+          node.must_equal Nodes::NotIn.new(attribute, [])
+        end
+
+        it 'can be constructed with a quoted infinite range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, ::Float::INFINITY, false))
+
+          node.must_equal Nodes::NotIn.new(attribute, [])
+        end
+
+
+        it 'can be constructed with a range ending at Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(0..::Float::INFINITY)
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(0, attribute)
+          )
+        end
+
+        it 'can be constructed with a quoted range ending at Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(0, ::Float::INFINITY, false))
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Quoted.new(0)
+          )
+        end
+
+        it 'can be constructed with an exclusive range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(0...3)
+
+          node.must_equal Nodes::And.new([
+            Nodes::GreaterThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            ),
+            Nodes::LessThan.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ])
+        end
+
+        def quoted_range(begin_val, end_val, exclude)
+          OpenStruct.new(
+            begin: Nodes::Quoted.new(begin_val),
+            end: Nodes::Quoted.new(end_val),
+            exclude_end?: exclude,
+          )
+        end
+      end
+
+      describe '#in' do
+        it 'can be constructed with a subquery' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(['%chunky%','%bacon%'])
+          attribute = Attribute.new nil, nil
+
+          node = attribute.in(mgr)
+
+          node.must_equal Nodes::In.new(attribute, mgr.ast)
+        end
+
+        it 'can be constructed with a list' do
+          attribute = Attribute.new nil, nil
+          node = attribute.in([1, 2, 3])
+
+          node.must_equal Nodes::In.new(
+            attribute,
+            [
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(2, attribute),
+              Nodes::Casted.new(3, attribute),
+            ]
+          )
+        end
+
+        it 'can be constructed with a random object' do
+          attribute = Attribute.new nil, nil
+          random_object = Object.new
+          node = attribute.in(random_object)
+
+          node.must_equal Nodes::In.new(
+            attribute,
+            Nodes::Casted.new(random_object, attribute)
+          )
+        end
+
+        it 'should generate IN in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in([1,2,3])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IN (1, 2, 3)
+          }
+        end
+      end
+
+      describe '#in_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].in_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in_any([[1,2], [3,4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" IN (1, 2) OR "users"."id" IN (3, 4))
+          }
+        end
+      end
+
+      describe '#in_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].in_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in_all([[1,2], [3,4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" IN (1, 2) AND "users"."id" IN (3, 4))
+          }
+        end
+      end
+
+      describe 'with a range' do
+        it 'can be constructed with a standard range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(1..3)
+
+          node.must_equal Nodes::Grouping.new(Nodes::Or.new(
+            Nodes::LessThan.new(
+              attribute,
+              Nodes::Casted.new(1, attribute)
+            ),
+            Nodes::GreaterThan.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ))
+        end
+
+        it 'can be constructed with a range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY..3)
+
+          node.must_equal Nodes::GreaterThan.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it 'can be constructed with an exclusive range starting from -Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY...3)
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it 'can be constructed with an infinite range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY..::Float::INFINITY)
+
+          node.must_equal Nodes::In.new(attribute, [])
+        end
+
+        it 'can be constructed with a range ending at Infinity' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(0..::Float::INFINITY)
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Casted.new(0, attribute)
+          )
+        end
+
+        it 'can be constructed with an exclusive range' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(0...3)
+
+          node.must_equal Nodes::Grouping.new(Nodes::Or.new(
+            Nodes::LessThan.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            ),
+            Nodes::GreaterThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ))
+        end
+      end
+
+      describe '#not_in' do
+        it 'can be constructed with a subquery' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(['%chunky%','%bacon%'])
+          attribute = Attribute.new nil, nil
+
+          node = attribute.not_in(mgr)
+
+          node.must_equal Nodes::NotIn.new(attribute, mgr.ast)
+        end
+
+        it 'can be constructed with a Union' do
+          relation = Table.new(:users)
+          mgr1 = relation.project(relation[:id])
+          mgr2 = relation.project(relation[:id])
+
+          union = mgr1.union(mgr2)
+          node = relation[:id].in(union)
+          node.to_sql.must_be_like %{
+            "users"."id" IN (( SELECT "users"."id" FROM "users" UNION SELECT "users"."id" FROM "users" ))
+          }
+        end
+
+        it 'can be constructed with a list' do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_in([1, 2, 3])
+
+          node.must_equal Nodes::NotIn.new(
+            attribute,
+            [
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(2, attribute),
+              Nodes::Casted.new(3, attribute),
+            ]
+          )
+        end
+
+        it 'can be constructed with a random object' do
+          attribute = Attribute.new nil, nil
+          random_object = Object.new
+          node = attribute.not_in(random_object)
+
+          node.must_equal Nodes::NotIn.new(
+            attribute,
+            Nodes::Casted.new(random_object, attribute)
+          )
+        end
+
+        it 'should generate NOT IN in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in([1,2,3])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" NOT IN (1, 2, 3)
+          }
+        end
+      end
+
+      describe '#not_in_any' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].not_in_any([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ORs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in_any([[1,2], [3,4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" NOT IN (1, 2) OR "users"."id" NOT IN (3, 4))
+          }
+        end
+      end
+
+      describe '#not_in_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].not_in_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in_all([[1,2], [3,4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" NOT IN (1, 2) AND "users"."id" NOT IN (3, 4))
+          }
+        end
+      end
+
+      describe '#eq_all' do
+        it 'should create a Grouping node' do
+          relation = Table.new(:users)
+          relation[:id].eq_all([1,2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it 'should generate ANDs in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_all([1,2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 AND "users"."id" = 2)
+          }
+        end
+      end
+
+      describe '#asc' do
+        it 'should create an Ascending node' do
+          relation = Table.new(:users)
+          relation[:id].asc.must_be_kind_of Nodes::Ascending
+        end
+
+        it 'should generate ASC in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.order relation[:id].asc
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" ORDER BY "users"."id" ASC
+          }
+        end
+      end
+
+      describe '#desc' do
+        it 'should create a Descending node' do
+          relation = Table.new(:users)
+          relation[:id].desc.must_be_kind_of Nodes::Descending
+        end
+
+        it 'should generate DESC in sql' do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.order relation[:id].desc
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" ORDER BY "users"."id" DESC
+          }
+        end
+      end
+
+      describe 'equality' do
+        describe '#to_sql' do
+          it 'should produce sql' do
+            table = Table.new :users
+            condition = table['id'].eq 1
+            condition.to_sql.must_equal '"users"."id" = 1'
+          end
+        end
+      end
+
+      describe 'type casting' do
+        it 'does not type cast by default' do
+          table = Table.new(:foo)
+          condition = table["id"].eq("1")
+
+          refute table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = '1')
+        end
+
+        it 'type casts when given an explicit caster' do
+          fake_caster = Object.new
+          def fake_caster.type_cast_for_database(attr_name, value)
+            if attr_name == "id"
+              value.to_i
+            else
+              value
+            end
+          end
+          table = Table.new(:foo, type_caster: fake_caster)
+          condition = table["id"].eq("1").and(table["other_id"].eq("2"))
+
+          assert table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = 1 AND "foo"."other_id" = '2')
+        end
+
+        it 'does not type cast SqlLiteral nodes' do
+          fake_caster = Object.new
+          def fake_caster.type_cast_for_database(attr_name, value)
+            value.to_i
+          end
+          table = Table.new(:foo, type_caster: fake_caster)
+          condition = table["id"].eq(Arel.sql("(select 1)"))
+
+          assert table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = (select 1))
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/attributes_test.rb b/activerecord/test/cases/arel/attributes_test.rb
new file mode 100644
index 0000000000..e17a6f5fd2
--- /dev/null
+++ b/activerecord/test/cases/arel/attributes_test.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  describe 'Attributes' do
+    it 'responds to lower' do
+      relation  = Table.new(:users)
+      attribute = relation[:foo]
+      node      = attribute.lower
+      assert_equal 'LOWER', node.name
+      assert_equal [attribute], node.expressions
+    end
+
+    describe 'equality' do
+      it 'is equal with equal ivars' do
+        array = [Attribute.new('foo', 'bar'), Attribute.new('foo', 'bar')]
+        assert_equal 1, array.uniq.size
+      end
+
+      it 'is not equal with different ivars' do
+        array = [Attribute.new('foo', 'bar'), Attribute.new('foo', 'baz')]
+        assert_equal 2, array.uniq.size
+      end
+    end
+
+    describe 'for' do
+      it 'deals with unknown column types' do
+        column = Struct.new(:type).new :crazy
+        Attributes.for(column).must_equal Attributes::Undefined
+      end
+
+      it 'returns the correct constant for strings' do
+        [:string, :text, :binary].each do |type|
+          column = Struct.new(:type).new type
+          Attributes.for(column).must_equal Attributes::String
+        end
+      end
+
+      it 'returns the correct constant for ints' do
+        column = Struct.new(:type).new :integer
+        Attributes.for(column).must_equal Attributes::Integer
+      end
+
+      it 'returns the correct constant for floats' do
+        column = Struct.new(:type).new :float
+        Attributes.for(column).must_equal Attributes::Float
+      end
+
+      it 'returns the correct constant for decimals' do
+        column = Struct.new(:type).new :decimal
+        Attributes.for(column).must_equal Attributes::Decimal
+      end
+
+      it 'returns the correct constant for boolean' do
+        column = Struct.new(:type).new :boolean
+        Attributes.for(column).must_equal Attributes::Boolean
+      end
+
+      it 'returns the correct constant for time' do
+        [:date, :datetime, :timestamp, :time].each do |type|
+          column = Struct.new(:type).new type
+          Attributes.for(column).must_equal Attributes::Time
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/bind_test.rb b/activerecord/test/cases/arel/collectors/bind_test.rb
new file mode 100644
index 0000000000..febc7290a7
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/bind_test.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Collectors
+    class TestBind < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect node
+        @visitor.accept(node, Collectors::Bind.new)
+      end
+
+      def compile node
+        collect(node).value
+      end
+
+      def ast_with_binds bvs
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.where(table[:name].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.ast
+      end
+
+      def test_compile_gathers_all_bind_params
+        binds = compile(ast_with_binds(["hello", "world"]))
+        assert_equal ["hello", "world"], binds
+
+        binds = compile(ast_with_binds(["hello2", "world3"]))
+        assert_equal ["hello2", "world3"], binds
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/composite_test.rb b/activerecord/test/cases/arel/collectors/composite_test.rb
new file mode 100644
index 0000000000..e330cae7a6
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/composite_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+require 'arel/collectors/bind'
+require 'arel/collectors/composite'
+
+module Arel
+  module Collectors
+    class TestComposite < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect node
+        sql_collector = Collectors::SQLString.new
+        bind_collector = Collectors::Bind.new
+        collector = Collectors::Composite.new(sql_collector, bind_collector)
+        @visitor.accept(node, collector)
+      end
+
+      def compile node
+        collect(node).value
+      end
+
+      def ast_with_binds bvs
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.where(table[:name].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.ast
+      end
+
+      def test_composite_collector_performs_multiple_collections_at_once
+        sql, binds = compile(ast_with_binds(["hello", "world"]))
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+        assert_equal ["hello", "world"], binds
+
+        sql, binds = compile(ast_with_binds(["hello2", "world3"]))
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+        assert_equal ["hello2", "world3"], binds
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/sql_string_test.rb b/activerecord/test/cases/arel/collectors/sql_string_test.rb
new file mode 100644
index 0000000000..a8ed3eb625
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/sql_string_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Collectors
+    class TestSqlString < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect node
+        @visitor.accept(node, Collectors::SQLString.new)
+      end
+
+      def compile node
+        collect(node).value
+      end
+
+      def ast_with_binds bv
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(bv))
+        manager.where(table[:name].eq(bv))
+        manager.ast
+      end
+
+      def test_compile
+        bv = Nodes::BindParam.new(1)
+        collector = collect ast_with_binds bv
+
+        sql = collector.compile ["hello", "world"]
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+      end
+
+      def test_returned_sql_uses_utf8_encoding
+        bv = Nodes::BindParam.new(1)
+        collector = collect ast_with_binds bv
+
+        sql = collector.compile ["hello", "world"]
+        assert_equal sql.encoding, Encoding::UTF_8
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb b/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb
new file mode 100644
index 0000000000..18f0ac14de
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+require_relative '../helper'
+require 'arel/collectors/substitute_binds'
+require 'arel/collectors/sql_string'
+
+module Arel
+  module Collectors
+    class TestSubstituteBindCollector < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def ast_with_binds
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new("hello")))
+        manager.where(table[:name].eq(Nodes::BindParam.new("world")))
+        manager.ast
+      end
+
+      def compile(node, quoter)
+        collector = Collectors::SubstituteBinds.new(quoter, Collectors::SQLString.new)
+        @visitor.accept(node, collector).value
+      end
+
+      def test_compile
+        quoter = Object.new
+        def quoter.quote(val)
+          val.to_s
+        end
+        sql = compile(ast_with_binds, quoter)
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = hello AND "users"."name" = world', sql
+      end
+
+      def test_quoting_is_delegated_to_quoter
+        quoter = Object.new
+        def quoter.quote(val)
+          val.inspect
+        end
+        sql = compile(ast_with_binds, quoter)
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = "hello" AND "users"."name" = "world"', sql
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/crud_test.rb b/activerecord/test/cases/arel/crud_test.rb
new file mode 100644
index 0000000000..38a956b9dd
--- /dev/null
+++ b/activerecord/test/cases/arel/crud_test.rb
@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  class FakeCrudder < SelectManager
+    class FakeEngine
+      attr_reader :calls, :connection_pool, :spec, :config
+
+      def initialize
+        @calls = []
+        @connection_pool = self
+        @spec = self
+        @config =  { :adapter => 'sqlite3' }
+      end
+
+      def connection; self end
+
+      def method_missing name, *args
+        @calls << [name, args]
+      end
+    end
+
+    include Crud
+
+    attr_reader :engine
+    attr_accessor :ctx
+
+    def initialize engine = FakeEngine.new
+      super
+    end
+  end
+
+  describe 'crud' do
+    describe 'insert' do
+      it 'should call insert on the connection' do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        im = fc.compile_insert [[table[:id], 'foo']]
+        assert_instance_of Arel::InsertManager, im
+      end
+    end
+
+    describe 'update' do
+      it 'should call update on the connection' do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        stmt = fc.compile_update [[table[:id], 'foo']], Arel::Attributes::Attribute.new(table, 'id')
+        assert_instance_of Arel::UpdateManager, stmt
+      end
+    end
+
+    describe 'delete' do
+      it 'should call delete on the connection' do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        stmt = fc.compile_delete
+        assert_instance_of Arel::DeleteManager, stmt
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/delete_manager_test.rb b/activerecord/test/cases/arel/delete_manager_test.rb
new file mode 100644
index 0000000000..36d482f10b
--- /dev/null
+++ b/activerecord/test/cases/arel/delete_manager_test.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  class DeleteManagerTest < Arel::Spec
+    describe 'new' do
+      it 'takes an engine' do
+        Arel::DeleteManager.new
+      end
+    end
+
+    it 'handles limit properly' do
+      table = Table.new(:users)
+      dm = Arel::DeleteManager.new
+      dm.take 10
+      dm.from table
+      assert_match(/LIMIT 10/, dm.to_sql)
+    end
+
+    describe 'from' do
+      it 'uses from' do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from table
+        dm.to_sql.must_be_like %{ DELETE FROM "users" }
+      end
+
+      it 'chains' do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from(table).must_equal dm
+      end
+    end
+
+    describe 'where' do
+      it 'uses where values' do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from table
+        dm.where table[:id].eq(10)
+        dm.to_sql.must_be_like %{ DELETE FROM "users" WHERE "users"."id" = 10}
+      end
+
+      it 'chains' do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.where(table[:id].eq(10)).must_equal dm
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/factory_methods_test.rb b/activerecord/test/cases/arel/factory_methods_test.rb
new file mode 100644
index 0000000000..2600b81e31
--- /dev/null
+++ b/activerecord/test/cases/arel/factory_methods_test.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  module FactoryMethods
+    class TestFactoryMethods < Arel::Test
+      class Factory
+        include Arel::FactoryMethods
+      end
+
+      def setup
+        @factory = Factory.new
+      end
+
+      def test_create_join
+        join = @factory.create_join :one, :two
+        assert_kind_of Nodes::Join, join
+        assert_equal :two, join.right
+      end
+
+      def test_create_on
+        on = @factory.create_on :one
+        assert_instance_of Nodes::On, on
+        assert_equal :one, on.expr
+      end
+
+      def test_create_true
+        true_node = @factory.create_true
+        assert_instance_of Nodes::True, true_node
+      end
+
+      def test_create_false
+        false_node = @factory.create_false
+        assert_instance_of Nodes::False, false_node
+      end
+
+      def test_lower
+        lower = @factory.lower :one
+        assert_instance_of Nodes::NamedFunction, lower
+        assert_equal 'LOWER', lower.name
+        assert_equal [:one], lower.expressions.map(&:expr)
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/helper.rb b/activerecord/test/cases/arel/helper.rb
new file mode 100644
index 0000000000..b716ee833f
--- /dev/null
+++ b/activerecord/test/cases/arel/helper.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+require 'rubygems'
+require 'minitest/autorun'
+require 'arel'
+
+require_relative 'support/fake_record'
+
+class Object
+  def must_be_like other
+    gsub(/\s+/, ' ').strip.must_equal other.gsub(/\s+/, ' ').strip
+  end
+end
+
+module Arel
+  class Test < Minitest::Test
+    def setup
+      super
+      @arel_engine = Arel::Table.engine
+      Arel::Table.engine = FakeRecord::Base.new
+    end
+
+    def teardown
+      Arel::Table.engine = @arel_engine if defined? @arel_engine
+      super
+    end
+
+    def assert_like expected, actual
+      assert_equal expected.gsub(/\s+/, ' ').strip,
+                   actual.gsub(/\s+/, ' ').strip
+    end
+  end
+
+  class Spec < Minitest::Spec
+    before do
+      @arel_engine = Arel::Table.engine
+      Arel::Table.engine = FakeRecord::Base.new
+    end
+
+    after do
+      Arel::Table.engine = @arel_engine if defined? @arel_engine
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/insert_manager_test.rb b/activerecord/test/cases/arel/insert_manager_test.rb
new file mode 100644
index 0000000000..33fab63fbc
--- /dev/null
+++ b/activerecord/test/cases/arel/insert_manager_test.rb
@@ -0,0 +1,244 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  class InsertManagerTest < Arel::Spec
+    describe 'new' do
+      it 'takes an engine' do
+        Arel::InsertManager.new
+      end
+    end
+
+    describe 'insert' do
+      it 'can create a Values node' do
+        manager = Arel::InsertManager.new
+        values  = manager.create_values %w{ a b }, %w{ c d }
+
+        assert_kind_of Arel::Nodes::Values, values
+        assert_equal %w{ a b }, values.left
+        assert_equal %w{ c d }, values.right
+      end
+
+      it 'allows sql literals' do
+        manager        = Arel::InsertManager.new
+        manager.into Table.new(:users)
+        manager.values = manager.create_values [Arel.sql('*')], %w{ a }
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" VALUES (*)
+        }
+      end
+
+      it 'works with multiple values' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          %w{1 david},
+          %w{2 kir},
+          ["3", Arel.sql('DEFAULT')],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"id\", \"name\") VALUES ('1', 'david'), ('2', 'kir'), ('3', DEFAULT)
+        }
+      end
+
+      it 'literals in multiple values are not escaped' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          [Arel.sql('*')],
+          [Arel.sql('DEFAULT')],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"name\") VALUES (*), (DEFAULT)
+        }
+      end
+
+      it 'works with multiple single values' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          %w{david},
+          %w{kir},
+          [Arel.sql('DEFAULT')],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"name\") VALUES ('david'), ('kir'), (DEFAULT)
+        }
+      end
+
+      it "inserts false" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+
+        manager.insert [[table[:bool], false]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("bool") VALUES ('f')
+        }
+      end
+
+      it "inserts null" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], nil]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id") VALUES (NULL)
+        }
+      end
+
+      it "inserts time" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+
+        time = Time.now
+        attribute = table[:created_at]
+
+        manager.insert [[attribute, time]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("created_at") VALUES (#{Table.engine.connection.quote time})
+        }
+      end
+
+      it 'takes a list of lists' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.insert [[table[:id], 1], [table[:name], 'aaron']]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+
+      it 'defaults the table' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], 1], [table[:name], 'aaron']]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+
+      it 'noop for empty list' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], 1]]
+        manager.insert []
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id") VALUES (1)
+        }
+      end
+
+      it 'is chainable' do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        insert_result = manager.insert [[table[:id],1]]
+        assert_equal manager, insert_result
+      end
+    end
+
+    describe 'into' do
+      it 'takes a Table and chains' do
+        manager = Arel::InsertManager.new
+        manager.into(Table.new(:users)).must_equal manager
+      end
+
+      it 'converts to sql' do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users"
+        }
+      end
+    end
+
+    describe 'columns' do
+      it "converts to sql" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.columns << table[:id]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id")
+        }
+      end
+    end
+
+    describe "values" do
+      it "converts to sql" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Nodes::Values.new [1]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" VALUES (1)
+        }
+      end
+
+      it "accepts sql literals" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Arel.sql("DEFAULT VALUES")
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" DEFAULT VALUES
+        }
+      end
+    end
+
+    describe "combo" do
+      it "combines columns and values list in order" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Nodes::Values.new [1, 'aaron']
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+    end
+
+    describe "select" do
+
+      it "accepts a select query in place of a VALUES clause" do
+        table   = Table.new :users
+
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        select = Arel::SelectManager.new
+        select.project Arel.sql('1')
+        select.project Arel.sql('"aaron"')
+
+        manager.select select
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") (SELECT 1, "aaron")
+        }
+      end
+
+    end
+
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/and_test.rb b/activerecord/test/cases/arel/nodes/and_test.rb
new file mode 100644
index 0000000000..de63e0bb31
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/and_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'And' do
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [And.new(['foo', 'bar']), And.new(['foo', 'bar'])]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [And.new(['foo', 'bar']), And.new(['foo', 'baz'])]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+
diff --git a/activerecord/test/cases/arel/nodes/as_test.rb b/activerecord/test/cases/arel/nodes/as_test.rb
new file mode 100644
index 0000000000..09c8aa8d62
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/as_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'As' do
+      describe '#as' do
+        it 'makes an AS node' do
+          attr = Table.new(:users)[:id]
+          as = attr.as(Arel.sql('foo'))
+          assert_equal attr, as.left
+          assert_equal 'foo', as.right
+        end
+
+        it 'converts right to SqlLiteral if a string' do
+          attr = Table.new(:users)[:id]
+          as = attr.as('foo')
+          assert_kind_of Arel::Nodes::SqlLiteral, as.right
+        end
+      end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [As.new('foo', 'bar'), As.new('foo', 'bar')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [As.new('foo', 'bar'), As.new('foo', 'baz')]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/ascending_test.rb b/activerecord/test/cases/arel/nodes/ascending_test.rb
new file mode 100644
index 0000000000..5c73e69fa5
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/ascending_test.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestAscending < Arel::Test
+      def test_construct
+        ascending = Ascending.new 'zomg'
+        assert_equal 'zomg', ascending.expr
+      end
+
+      def test_reverse
+        ascending = Ascending.new 'zomg'
+        descending = ascending.reverse
+        assert_kind_of Descending, descending
+        assert_equal ascending.expr, descending.expr
+      end
+
+      def test_direction
+        ascending = Ascending.new 'zomg'
+        assert_equal :asc, ascending.direction
+      end
+
+      def test_ascending?
+        ascending = Ascending.new 'zomg'
+        assert ascending.ascending?
+      end
+
+      def test_descending?
+        ascending = Ascending.new 'zomg'
+        assert !ascending.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [Ascending.new('zomg'), Ascending.new('zomg')]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Ascending.new('zomg'), Ascending.new('zomg!')]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/bin_test.rb b/activerecord/test/cases/arel/nodes/bin_test.rb
new file mode 100644
index 0000000000..923a296adf
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/bin_test.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestBin < Arel::Test
+      def test_new
+        assert Arel::Nodes::Bin.new('zomg')
+      end
+
+      def test_default_to_sql
+        viz  = Arel::Visitors::ToSql.new Table.engine.connection_pool
+        node = Arel::Nodes::Bin.new(Arel.sql('zomg'))
+        assert_equal 'zomg', viz.accept(node, Collectors::SQLString.new).value
+      end
+
+      def test_mysql_to_sql
+        viz  = Arel::Visitors::MySQL.new Table.engine.connection_pool
+        node = Arel::Nodes::Bin.new(Arel.sql('zomg'))
+        assert_equal 'BINARY zomg', viz.accept(node, Collectors::SQLString.new).value
+      end
+
+      def test_equality_with_same_ivars
+        array = [Bin.new('zomg'), Bin.new('zomg')]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Bin.new('zomg'), Bin.new('zomg!')]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/binary_test.rb b/activerecord/test/cases/arel/nodes/binary_test.rb
new file mode 100644
index 0000000000..0bea35f7dd
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/binary_test.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'Binary' do
+      describe '#hash' do
+        it 'generates a hash based on its value' do
+          eq = Equality.new('foo', 'bar')
+          eq2 = Equality.new('foo', 'bar')
+          eq3 = Equality.new('bar', 'baz')
+
+          assert_equal eq.hash, eq2.hash
+          refute_equal eq.hash, eq3.hash
+        end
+
+        it 'generates a hash specific to its class' do
+          eq = Equality.new('foo', 'bar')
+          neq = NotEqual.new('foo', 'bar')
+
+          refute_equal eq.hash, neq.hash
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/bind_param_test.rb b/activerecord/test/cases/arel/nodes/bind_param_test.rb
new file mode 100644
index 0000000000..665581edce
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/bind_param_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'BindParam' do
+      it 'is equal to other bind params with the same value' do
+        BindParam.new(1).must_equal(BindParam.new(1))
+        BindParam.new("foo").must_equal(BindParam.new("foo"))
+      end
+
+      it 'is not equal to other nodes' do
+        BindParam.new(nil).wont_equal(Node.new)
+      end
+
+      it 'is not equal to bind params with different values' do
+        BindParam.new(1).wont_equal(BindParam.new(2))
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/case_test.rb b/activerecord/test/cases/arel/nodes/case_test.rb
new file mode 100644
index 0000000000..70364fe6ab
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/case_test.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'Case' do
+      describe '#initialize' do
+        it 'sets case expression from first argument' do
+          node = Case.new 'foo'
+
+          assert_equal 'foo', node.case
+        end
+
+        it 'sets default case from second argument' do
+          node = Case.new nil, 'bar'
+
+          assert_equal 'bar', node.default
+        end
+      end
+
+      describe '#clone' do
+        it 'clones case, conditions and default' do
+          foo = Nodes.build_quoted 'foo'
+
+          node = Case.new
+          node.case = foo
+          node.conditions = [When.new(foo, foo)]
+          node.default = foo
+
+          dolly = node.clone
+
+          assert_equal dolly.case, node.case
+          refute_same  dolly.case, node.case
+
+          assert_equal dolly.conditions, node.conditions
+          refute_same  dolly.conditions, node.conditions
+
+          assert_equal dolly.default, node.default
+          refute_same  dolly.default, node.default
+        end
+      end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          foo = Nodes.build_quoted 'foo'
+          one = Nodes.build_quoted 1
+          zero = Nodes.build_quoted 0
+
+          case1 = Case.new foo
+          case1.conditions = [When.new(foo, one)]
+          case1.default = Else.new zero
+
+          case2 = Case.new foo
+          case2.conditions = [When.new(foo, one)]
+          case2.default = Else.new zero
+
+          array = [case1, case2]
+
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          foo = Nodes.build_quoted 'foo'
+          bar = Nodes.build_quoted 'bar'
+          one = Nodes.build_quoted 1
+          zero = Nodes.build_quoted 0
+
+          case1 = Case.new foo
+          case1.conditions = [When.new(foo, one)]
+          case1.default = Else.new zero
+
+          case2 = Case.new foo
+          case2.conditions = [When.new(bar, one)]
+          case2.default = Else.new zero
+
+          array = [case1, case2]
+
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/casted_test.rb b/activerecord/test/cases/arel/nodes/casted_test.rb
new file mode 100644
index 0000000000..a6e2dd2294
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/casted_test.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe Casted do
+      describe '#hash' do
+        it 'is equal when eql? returns true' do
+          one = Casted.new 1, 2
+          also_one = Casted.new 1, 2
+
+          assert_equal one.hash, also_one.hash
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/count_test.rb b/activerecord/test/cases/arel/nodes/count_test.rb
new file mode 100644
index 0000000000..28d8481993
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/count_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+class Arel::Nodes::CountTest < Arel::Spec
+  describe "as" do
+    it 'should alias the count' do
+      table = Arel::Table.new :users
+      table[:id].count.as('foo').to_sql.must_be_like %{
+        COUNT("users"."id") AS foo
+      }
+    end
+  end
+
+  describe "eq" do
+    it "should compare the count" do
+      table = Arel::Table.new :users
+      table[:id].count.eq(2).to_sql.must_be_like %{
+        COUNT("users"."id") = 2
+      }
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      array = [Arel::Nodes::Count.new('foo'), Arel::Nodes::Count.new('foo')]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      array = [Arel::Nodes::Count.new('foo'), Arel::Nodes::Count.new('foo!')]
+      assert_equal 2, array.uniq.size
+    end
+  end
+
+  describe 'math' do
+    it 'allows mathematical functions' do
+      table = Arel::Table.new :users
+      (table[:id].count + 1).to_sql.must_be_like %{
+        (COUNT("users"."id") + 1)
+      }
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/delete_statement_test.rb b/activerecord/test/cases/arel/nodes/delete_statement_test.rb
new file mode 100644
index 0000000000..ada8964646
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/delete_statement_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+describe Arel::Nodes::DeleteStatement do
+  describe "#clone" do
+    it "clones wheres" do
+      statement = Arel::Nodes::DeleteStatement.new
+      statement.wheres = %w[a b c]
+
+      dolly = statement.clone
+      dolly.wheres.must_equal statement.wheres
+      dolly.wheres.wont_be_same_as statement.wheres
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      statement1 = Arel::Nodes::DeleteStatement.new
+      statement1.wheres = %w[a b c]
+      statement2 = Arel::Nodes::DeleteStatement.new
+      statement2.wheres = %w[a b c]
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      statement1 = Arel::Nodes::DeleteStatement.new
+      statement1.wheres = %w[a b c]
+      statement2 = Arel::Nodes::DeleteStatement.new
+      statement2.wheres = %w[1 2 3]
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/descending_test.rb b/activerecord/test/cases/arel/nodes/descending_test.rb
new file mode 100644
index 0000000000..5fe0ba62b0
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/descending_test.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestDescending < Arel::Test
+      def test_construct
+        descending = Descending.new 'zomg'
+        assert_equal 'zomg', descending.expr
+      end
+
+      def test_reverse
+        descending = Descending.new 'zomg'
+        ascending = descending.reverse
+        assert_kind_of Ascending, ascending
+        assert_equal descending.expr, ascending.expr
+      end
+
+      def test_direction
+        descending = Descending.new 'zomg'
+        assert_equal :desc, descending.direction
+      end
+
+      def test_ascending?
+        descending = Descending.new 'zomg'
+        assert !descending.ascending?
+      end
+
+      def test_descending?
+        descending = Descending.new 'zomg'
+        assert descending.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [Descending.new('zomg'), Descending.new('zomg')]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Descending.new('zomg'), Descending.new('zomg!')]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/distinct_test.rb b/activerecord/test/cases/arel/nodes/distinct_test.rb
new file mode 100644
index 0000000000..465700118e
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/distinct_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'Distinct' do
+      describe 'equality' do
+        it 'is equal to other distinct nodes' do
+          array = [Distinct.new, Distinct.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with other nodes' do
+          array = [Distinct.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+
diff --git a/activerecord/test/cases/arel/nodes/equality_test.rb b/activerecord/test/cases/arel/nodes/equality_test.rb
new file mode 100644
index 0000000000..28a74de321
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/equality_test.rb
@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'equality' do
+      # FIXME: backwards compat
+      describe 'backwards compat' do
+        describe 'operator' do
+          it 'returns :==' do
+            attr = Table.new(:users)[:id]
+            left  = attr.eq(10)
+            left.operator.must_equal :==
+          end
+        end
+
+        describe 'operand1' do
+          it "should equal left" do
+            attr = Table.new(:users)[:id]
+            left  = attr.eq(10)
+            left.left.must_equal left.operand1
+          end
+        end
+
+        describe 'operand2' do
+          it "should equal right" do
+            attr = Table.new(:users)[:id]
+            left  = attr.eq(10)
+            left.right.must_equal left.operand2
+          end
+        end
+
+        describe 'to_sql' do
+          it 'takes an engine' do
+            engine = FakeRecord::Base.new
+            engine.connection.extend Module.new {
+              attr_accessor :quote_count
+              def quote(*args) @quote_count += 1; super; end
+              def quote_column_name(*args) @quote_count += 1; super; end
+              def quote_table_name(*args) @quote_count += 1; super; end
+            }
+            engine.connection.quote_count = 0
+
+            attr = Table.new(:users)[:id]
+            test = attr.eq(10)
+            test.to_sql engine
+            engine.connection.quote_count.must_equal 3
+          end
+        end
+      end
+
+      describe 'or' do
+        it 'makes an OR node' do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.or right
+          node.expr.left.must_equal left
+          node.expr.right.must_equal right
+        end
+      end
+
+      describe 'and' do
+        it 'makes and AND node' do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.and right
+          node.left.must_equal left
+          node.right.must_equal right
+        end
+      end
+
+      it 'is equal with equal ivars' do
+        array = [Equality.new('foo', 'bar'), Equality.new('foo', 'bar')]
+        assert_equal 1, array.uniq.size
+      end
+
+      it 'is not equal with different ivars' do
+        array = [Equality.new('foo', 'bar'), Equality.new('foo', 'baz')]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/extract_test.rb b/activerecord/test/cases/arel/nodes/extract_test.rb
new file mode 100644
index 0000000000..f6dc1626a4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/extract_test.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+class Arel::Nodes::ExtractTest < Arel::Spec
+  it "should extract field" do
+    table = Arel::Table.new :users
+    table[:timestamp].extract('date').to_sql.must_be_like %{
+      EXTRACT(DATE FROM "users"."timestamp")
+    }
+  end
+
+  describe "as" do
+    it 'should alias the extract' do
+      table = Arel::Table.new :users
+      table[:timestamp].extract('date').as('foo').to_sql.must_be_like %{
+        EXTRACT(DATE FROM "users"."timestamp") AS foo
+      }
+    end
+
+    it 'should not mutate the extract' do
+      table = Arel::Table.new :users
+      extract = table[:timestamp].extract('date')
+      before = extract.dup
+      extract.as('foo')
+      assert_equal extract, before
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      table = Arel::Table.new :users
+      array = [table[:attr].extract('foo'), table[:attr].extract('foo')]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      table = Arel::Table.new :users
+      array = [table[:attr].extract('foo'), table[:attr].extract('bar')]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/false_test.rb b/activerecord/test/cases/arel/nodes/false_test.rb
new file mode 100644
index 0000000000..8b91dc227c
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/false_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'False' do
+      describe 'equality' do
+        it 'is equal to other false nodes' do
+          array = [False.new, False.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with other nodes' do
+          array = [False.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+
diff --git a/activerecord/test/cases/arel/nodes/grouping_test.rb b/activerecord/test/cases/arel/nodes/grouping_test.rb
new file mode 100644
index 0000000000..7ad1584f0f
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/grouping_test.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class GroupingTest < Arel::Spec
+      it 'should create Equality nodes' do
+        grouping = Grouping.new(Nodes.build_quoted('foo'))
+        grouping.eq('foo').to_sql.must_be_like %q{('foo') = 'foo'}
+      end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [Grouping.new('foo'), Grouping.new('foo')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [Grouping.new('foo'), Grouping.new('bar')]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+
diff --git a/activerecord/test/cases/arel/nodes/infix_operation_test.rb b/activerecord/test/cases/arel/nodes/infix_operation_test.rb
new file mode 100644
index 0000000000..28a4710dc0
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/infix_operation_test.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestInfixOperation < Arel::Test
+      def test_construct
+        operation = InfixOperation.new :+, 1, 2
+        assert_equal :+, operation.operator
+        assert_equal 1, operation.left
+        assert_equal 2, operation.right
+      end
+
+      def test_operation_alias
+        operation = InfixOperation.new :+, 1, 2
+        aliaz = operation.as('zomg')
+        assert_kind_of As, aliaz
+        assert_equal operation, aliaz.left
+        assert_equal 'zomg', aliaz.right
+      end
+
+      def test_operation_ordering
+        operation = InfixOperation.new :+, 1, 2
+        ordering = operation.desc
+        assert_kind_of Descending, ordering
+        assert_equal operation, ordering.expr
+        assert ordering.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [InfixOperation.new(:+, 1, 2), InfixOperation.new(:+, 1, 2)]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [InfixOperation.new(:+, 1, 2), InfixOperation.new(:+, 1, 3)]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/insert_statement_test.rb b/activerecord/test/cases/arel/nodes/insert_statement_test.rb
new file mode 100644
index 0000000000..87f9d83a32
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/insert_statement_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+describe Arel::Nodes::InsertStatement do
+  describe "#clone" do
+    it "clones columns and values" do
+      statement = Arel::Nodes::InsertStatement.new
+      statement.columns = %w[a b c]
+      statement.values  = %w[x y z]
+
+      dolly = statement.clone
+      dolly.columns.must_equal statement.columns
+      dolly.values.must_equal statement.values
+
+      dolly.columns.wont_be_same_as statement.columns
+      dolly.values.wont_be_same_as statement.values
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      statement1 = Arel::Nodes::InsertStatement.new
+      statement1.columns = %w[a b c]
+      statement1.values  = %w[x y z]
+      statement2 = Arel::Nodes::InsertStatement.new
+      statement2.columns = %w[a b c]
+      statement2.values  = %w[x y z]
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      statement1 = Arel::Nodes::InsertStatement.new
+      statement1.columns = %w[a b c]
+      statement1.values  = %w[x y z]
+      statement2 = Arel::Nodes::InsertStatement.new
+      statement2.columns = %w[a b c]
+      statement2.values  = %w[1 2 3]
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/named_function_test.rb b/activerecord/test/cases/arel/nodes/named_function_test.rb
new file mode 100644
index 0000000000..30f6dac595
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/named_function_test.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestNamedFunction < Arel::Test
+      def test_construct
+        function = NamedFunction.new 'omg', 'zomg'
+        assert_equal 'omg', function.name
+        assert_equal 'zomg', function.expressions
+      end
+
+      def test_function_alias
+        function = NamedFunction.new 'omg', 'zomg'
+        function = function.as('wth')
+        assert_equal 'omg', function.name
+        assert_equal 'zomg', function.expressions
+        assert_kind_of SqlLiteral, function.alias
+        assert_equal 'wth', function.alias
+      end
+
+      def test_construct_with_alias
+        function = NamedFunction.new 'omg', 'zomg', 'wth'
+        assert_equal 'omg', function.name
+        assert_equal 'zomg', function.expressions
+        assert_kind_of SqlLiteral, function.alias
+        assert_equal 'wth', function.alias
+      end
+
+      def test_equality_with_same_ivars
+        array = [
+          NamedFunction.new('omg', 'zomg', 'wth'),
+          NamedFunction.new('omg', 'zomg', 'wth')
+        ]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [
+          NamedFunction.new('omg', 'zomg', 'wth'),
+          NamedFunction.new('zomg', 'zomg', 'wth')
+        ]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/node_test.rb b/activerecord/test/cases/arel/nodes/node_test.rb
new file mode 100644
index 0000000000..c1d3a01d1c
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/node_test.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  class TestNode < Arel::Test
+    def test_includes_factory_methods
+      assert Node.new.respond_to?(:create_join)
+    end
+
+    def test_all_nodes_are_nodes
+      Nodes.constants.map { |k|
+        Nodes.const_get(k)
+      }.grep(Class).each do |klass|
+        next if Nodes::SqlLiteral == klass
+        next if Nodes::BindParam == klass
+        next if klass.name =~ /^Arel::Nodes::(?:Test|.*Test$)/
+        assert klass.ancestors.include?(Nodes::Node), klass.name
+      end
+    end
+
+    def test_each
+      list = []
+      node = Nodes::Node.new
+      node.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_generator
+      list = []
+      node = Nodes::Node.new
+      node.each.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_enumerable
+      node = Nodes::Node.new
+      assert_kind_of Enumerable, node
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/not_test.rb b/activerecord/test/cases/arel/nodes/not_test.rb
new file mode 100644
index 0000000000..15f94a6f10
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/not_test.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'not' do
+      describe '#not' do
+        it 'makes a NOT node' do
+          attr = Table.new(:users)[:id]
+          expr  = attr.eq(10)
+          node  = expr.not
+          node.must_be_kind_of Not
+          node.expr.must_equal expr
+        end
+      end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [Not.new('foo'), Not.new('foo')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [Not.new('foo'), Not.new('baz')]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/or_test.rb b/activerecord/test/cases/arel/nodes/or_test.rb
new file mode 100644
index 0000000000..4f8d56d165
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/or_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'or' do
+      describe '#or' do
+        it 'makes an OR node' do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.or right
+          node.expr.left.must_equal left
+          node.expr.right.must_equal right
+
+          oror = node.or(right)
+          oror.expr.left.must_equal node
+          oror.expr.right.must_equal right
+        end
+      end
+
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          array = [Or.new('foo', 'bar'), Or.new('foo', 'bar')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          array = [Or.new('foo', 'bar'), Or.new('foo', 'baz')]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/over_test.rb b/activerecord/test/cases/arel/nodes/over_test.rb
new file mode 100644
index 0000000000..c9804c395f
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/over_test.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+class Arel::Nodes::OverTest < Arel::Spec
+  describe 'as' do
+    it 'should alias the expression' do
+      table = Arel::Table.new :users
+      table[:id].count.over.as('foo').to_sql.must_be_like %{
+        COUNT("users"."id") OVER () AS foo
+      }
+    end
+  end
+
+  describe 'with literal' do
+    it 'should reference the window definition by name' do
+      table = Arel::Table.new :users
+      table[:id].count.over('foo').to_sql.must_be_like %{
+        COUNT("users"."id") OVER "foo"
+      }
+    end
+  end
+
+  describe 'with SQL literal' do
+    it 'should reference the window definition by name' do
+      table = Arel::Table.new :users
+      table[:id].count.over(Arel.sql('foo')).to_sql.must_be_like %{
+        COUNT("users"."id") OVER foo
+      }
+    end
+  end
+
+  describe 'with no expression' do
+    it 'should use empty definition' do
+      table = Arel::Table.new :users
+      table[:id].count.over.to_sql.must_be_like %{
+        COUNT("users"."id") OVER ()
+      }
+    end
+  end
+
+  describe 'with expression' do
+    it 'should use definition in sub-expression' do
+      table = Arel::Table.new :users
+      window = Arel::Nodes::Window.new.order(table['foo'])
+      table[:id].count.over(window).to_sql.must_be_like %{
+        COUNT("users"."id") OVER (ORDER BY \"users\".\"foo\")
+      }
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      array = [
+        Arel::Nodes::Over.new('foo', 'bar'),
+        Arel::Nodes::Over.new('foo', 'bar')
+      ]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      array = [
+        Arel::Nodes::Over.new('foo', 'bar'),
+        Arel::Nodes::Over.new('foo', 'baz')
+      ]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/select_core_test.rb b/activerecord/test/cases/arel/nodes/select_core_test.rb
new file mode 100644
index 0000000000..bbb06666b6
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/select_core_test.rb
@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestSelectCore < Arel::Test
+      def test_clone
+        core = Arel::Nodes::SelectCore.new
+        core.froms       = %w[a b c]
+        core.projections = %w[d e f]
+        core.wheres      = %w[g h i]
+
+        dolly = core.clone
+
+        assert_equal core.froms, dolly.froms
+        assert_equal core.projections, dolly.projections
+        assert_equal core.wheres, dolly.wheres
+
+        refute_same core.froms, dolly.froms
+        refute_same core.projections, dolly.projections
+        refute_same core.wheres, dolly.wheres
+      end
+
+      def test_set_quantifier
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::Distinct.new
+        viz = Arel::Visitors::ToSql.new Table.engine.connection_pool
+        assert_match 'DISTINCT', viz.accept(core, Collectors::SQLString.new).value
+      end
+
+      def test_equality_with_same_ivars
+        core1 = SelectCore.new
+        core1.froms       = %w[a b c]
+        core1.projections = %w[d e f]
+        core1.wheres      = %w[g h i]
+        core1.groups      = %w[j k l]
+        core1.windows     = %w[m n o]
+        core1.havings     = %w[p q r]
+        core2 = SelectCore.new
+        core2.froms       = %w[a b c]
+        core2.projections = %w[d e f]
+        core2.wheres      = %w[g h i]
+        core2.groups      = %w[j k l]
+        core2.windows     = %w[m n o]
+        core2.havings     = %w[p q r]
+        array = [core1, core2]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        core1 = SelectCore.new
+        core1.froms       = %w[a b c]
+        core1.projections = %w[d e f]
+        core1.wheres      = %w[g h i]
+        core1.groups      = %w[j k l]
+        core1.windows     = %w[m n o]
+        core1.havings     = %w[p q r]
+        core2 = SelectCore.new
+        core2.froms       = %w[a b c]
+        core2.projections = %w[d e f]
+        core2.wheres      = %w[g h i]
+        core2.groups      = %w[j k l]
+        core2.windows     = %w[m n o]
+        core2.havings     = %w[l o l]
+        array = [core1, core2]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/select_statement_test.rb b/activerecord/test/cases/arel/nodes/select_statement_test.rb
new file mode 100644
index 0000000000..5e313e03fa
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/select_statement_test.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+describe Arel::Nodes::SelectStatement do
+  describe "#clone" do
+    it "clones cores" do
+      statement = Arel::Nodes::SelectStatement.new %w[a b c]
+
+      dolly = statement.clone
+      dolly.cores.must_equal      statement.cores
+      dolly.cores.wont_be_same_as statement.cores
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      statement1 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement1.offset = 1
+      statement1.limit  = 2
+      statement1.lock   = false
+      statement1.orders = %w[x y z]
+      statement1.with   = 'zomg'
+      statement2 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement2.offset = 1
+      statement2.limit  = 2
+      statement2.lock   = false
+      statement2.orders = %w[x y z]
+      statement2.with   = 'zomg'
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      statement1 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement1.offset = 1
+      statement1.limit  = 2
+      statement1.lock   = false
+      statement1.orders = %w[x y z]
+      statement1.with   = 'zomg'
+      statement2 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement2.offset = 1
+      statement2.limit  = 2
+      statement2.lock   = false
+      statement2.orders = %w[x y z]
+      statement2.with   = 'wth'
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/sql_literal_test.rb b/activerecord/test/cases/arel/nodes/sql_literal_test.rb
new file mode 100644
index 0000000000..0c4f23be78
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/sql_literal_test.rb
@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+require_relative '../helper'
+require 'yaml'
+
+module Arel
+  module Nodes
+    class SqlLiteralTest < Arel::Spec
+      before do
+        @visitor = Visitors::ToSql.new Table.engine.connection
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      describe 'sql' do
+        it 'makes a sql literal node' do
+          sql = Arel.sql 'foo'
+          sql.must_be_kind_of Arel::Nodes::SqlLiteral
+        end
+      end
+
+      describe 'count' do
+        it 'makes a count node' do
+          node = SqlLiteral.new('*').count
+          compile(node).must_be_like %{ COUNT(*) }
+        end
+
+        it 'makes a distinct node' do
+          node = SqlLiteral.new('*').count true
+          compile(node).must_be_like %{ COUNT(DISTINCT *) }
+        end
+      end
+
+      describe 'equality' do
+        it 'makes an equality node' do
+          node = SqlLiteral.new('foo').eq(1)
+          compile(node).must_be_like %{ foo = 1 }
+        end
+
+        it 'is equal with equal contents' do
+          array = [SqlLiteral.new('foo'), SqlLiteral.new('foo')]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different contents' do
+          array = [SqlLiteral.new('foo'), SqlLiteral.new('bar')]
+          assert_equal 2, array.uniq.size
+        end
+      end
+
+      describe 'grouped "or" equality' do
+        it 'makes a grouping node with an or node' do
+          node = SqlLiteral.new('foo').eq_any([1,2])
+          compile(node).must_be_like %{ (foo = 1 OR foo = 2) }
+        end
+      end
+
+      describe 'grouped "and" equality' do
+        it 'makes a grouping node with an and node' do
+          node = SqlLiteral.new('foo').eq_all([1,2])
+          compile(node).must_be_like %{ (foo = 1 AND foo = 2) }
+        end
+      end
+
+      describe 'serialization' do
+        it 'serializes into YAML' do
+          yaml_literal = SqlLiteral.new('foo').to_yaml
+          assert_equal('foo', YAML.load(yaml_literal))
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/sum_test.rb b/activerecord/test/cases/arel/nodes/sum_test.rb
new file mode 100644
index 0000000000..46c908d872
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/sum_test.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+class Arel::Nodes::SumTest < Arel::Spec
+  describe "as" do
+    it 'should alias the sum' do
+      table = Arel::Table.new :users
+      table[:id].sum.as('foo').to_sql.must_be_like %{
+        SUM("users"."id") AS foo
+      }
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      array = [Arel::Nodes::Sum.new('foo'), Arel::Nodes::Sum.new('foo')]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      array = [Arel::Nodes::Sum.new('foo'), Arel::Nodes::Sum.new('foo!')]
+      assert_equal 2, array.uniq.size
+    end
+  end
+  
+  describe 'order' do
+    it 'should order the sum' do
+      table = Arel::Table.new :users
+      table[:id].sum.desc.to_sql.must_be_like %{
+        SUM("users"."id") DESC
+      }
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/table_alias_test.rb b/activerecord/test/cases/arel/nodes/table_alias_test.rb
new file mode 100644
index 0000000000..b1b49919d5
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/table_alias_test.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'table alias' do
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          relation1 = Table.new(:users)
+          node1     = TableAlias.new relation1, :foo
+          relation2 = Table.new(:users)
+          node2     = TableAlias.new relation2, :foo
+          array = [node1, node2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          relation1 = Table.new(:users)
+          node1     = TableAlias.new relation1, :foo
+          relation2 = Table.new(:users)
+          node2     = TableAlias.new relation2, :bar
+          array = [node1, node2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/true_test.rb b/activerecord/test/cases/arel/nodes/true_test.rb
new file mode 100644
index 0000000000..198e7b1aa4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/true_test.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'True' do
+      describe 'equality' do
+        it 'is equal to other true nodes' do
+          array = [True.new, True.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with other nodes' do
+          array = [True.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
+
+
diff --git a/activerecord/test/cases/arel/nodes/unary_operation_test.rb b/activerecord/test/cases/arel/nodes/unary_operation_test.rb
new file mode 100644
index 0000000000..e76b59c8e1
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/unary_operation_test.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    class TestUnaryOperation < Arel::Test
+      def test_construct
+        operation = UnaryOperation.new :-, 1
+        assert_equal :-, operation.operator
+        assert_equal 1, operation.expr
+      end
+
+      def test_operation_alias
+        operation = UnaryOperation.new :-, 1
+        aliaz = operation.as('zomg')
+        assert_kind_of As, aliaz
+        assert_equal operation, aliaz.left
+        assert_equal 'zomg', aliaz.right
+      end
+
+      def test_operation_ordering
+        operation = UnaryOperation.new :-, 1
+        ordering = operation.desc
+        assert_kind_of Descending, ordering
+        assert_equal operation, ordering.expr
+        assert ordering.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [UnaryOperation.new(:-, 1), UnaryOperation.new(:-, 1)]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [UnaryOperation.new(:-, 1), UnaryOperation.new(:-, 2)]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/update_statement_test.rb b/activerecord/test/cases/arel/nodes/update_statement_test.rb
new file mode 100644
index 0000000000..3a635f75d6
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/update_statement_test.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+describe Arel::Nodes::UpdateStatement do
+  describe "#clone" do
+    it "clones wheres and values" do
+      statement = Arel::Nodes::UpdateStatement.new
+      statement.wheres = %w[a b c]
+      statement.values = %w[x y z]
+
+      dolly = statement.clone
+      dolly.wheres.must_equal statement.wheres
+      dolly.wheres.wont_be_same_as statement.wheres
+
+      dolly.values.must_equal statement.values
+      dolly.values.wont_be_same_as statement.values
+    end
+  end
+
+  describe 'equality' do
+    it 'is equal with equal ivars' do
+      statement1 = Arel::Nodes::UpdateStatement.new
+      statement1.relation = 'zomg'
+      statement1.wheres   = 2
+      statement1.values   = false
+      statement1.orders   = %w[x y z]
+      statement1.limit    = 42
+      statement1.key      = 'zomg'
+      statement2 = Arel::Nodes::UpdateStatement.new
+      statement2.relation = 'zomg'
+      statement2.wheres   = 2
+      statement2.values   = false
+      statement2.orders   = %w[x y z]
+      statement2.limit    = 42
+      statement2.key      = 'zomg'
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it 'is not equal with different ivars' do
+      statement1 = Arel::Nodes::UpdateStatement.new
+      statement1.relation = 'zomg'
+      statement1.wheres   = 2
+      statement1.values   = false
+      statement1.orders   = %w[x y z]
+      statement1.limit    = 42
+      statement1.key      = 'zomg'
+      statement2 = Arel::Nodes::UpdateStatement.new
+      statement2.relation = 'zomg'
+      statement2.wheres   = 2
+      statement2.values   = false
+      statement2.orders   = %w[x y z]
+      statement2.limit    = 42
+      statement2.key      = 'wth'
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/window_test.rb b/activerecord/test/cases/arel/nodes/window_test.rb
new file mode 100644
index 0000000000..81ecd5ced8
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/window_test.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Nodes
+    describe 'Window' do
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          window1 = Window.new
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = Window.new
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          window1 = Window.new
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = Window.new
+          window2.orders = [1, 2]
+          window1.partitions = [1]
+          window2.frame 4
+          array = [window1, window2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+
+    describe 'NamedWindow' do
+      describe 'equality' do
+        it 'is equal with equal ivars' do
+          window1 = NamedWindow.new 'foo'
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = NamedWindow.new 'foo'
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with different ivars' do
+          window1 = NamedWindow.new 'foo'
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = NamedWindow.new 'bar'
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+
+    describe 'CurrentRow' do
+      describe 'equality' do
+        it 'is equal to other current row nodes' do
+          array = [CurrentRow.new, CurrentRow.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it 'is not equal with other nodes' do
+          array = [CurrentRow.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes_test.rb b/activerecord/test/cases/arel/nodes_test.rb
new file mode 100644
index 0000000000..1934ef4c3b
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  module Nodes
+    class TestNodes < Arel::Test
+      def test_every_arel_nodes_have_hash_eql_eqeq_from_same_class
+        # #descendants code from activesupport
+        node_descendants = []
+        ObjectSpace.each_object(Arel::Nodes::Node.singleton_class) do |k|
+          next if k.respond_to?(:singleton_class?) && k.singleton_class?
+          node_descendants.unshift k unless k == self
+        end
+        node_descendants.delete(Arel::Nodes::Node)
+        node_descendants.delete(Arel::Nodes::NodeExpression)
+
+        bad_node_descendants = node_descendants.reject do |subnode|
+          eqeq_owner = subnode.instance_method(:==).owner
+          eql_owner = subnode.instance_method(:eql?).owner
+          hash_owner = subnode.instance_method(:hash).owner
+
+          eqeq_owner < Arel::Nodes::Node &&
+              eqeq_owner == eql_owner &&
+              eqeq_owner == hash_owner
+        end
+
+        problem_msg = 'Some subclasses of Arel::Nodes::Node do not have a' \
+            ' #== or #eql? or #hash defined from the same class as the others'
+        assert_empty bad_node_descendants, problem_msg
+      end
+
+
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/select_manager_test.rb b/activerecord/test/cases/arel/select_manager_test.rb
new file mode 100644
index 0000000000..e9056953d8
--- /dev/null
+++ b/activerecord/test/cases/arel/select_manager_test.rb
@@ -0,0 +1,1236 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+
+  class SelectManagerTest < Arel::Spec
+    def test_join_sources
+      manager = Arel::SelectManager.new
+      manager.join_sources << Arel::Nodes::StringJoin.new(Nodes.build_quoted('foo'))
+      assert_equal "SELECT FROM 'foo'", manager.to_sql
+    end
+
+    describe 'backwards compatibility' do
+      describe 'project' do
+        it 'accepts symbols as sql literals' do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.project :id
+          manager.from table
+          manager.to_sql.must_be_like %{
+            SELECT id FROM "users"
+          }
+        end
+      end
+
+      describe 'order' do
+        it 'accepts symbols' do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.project Nodes::SqlLiteral.new '*'
+          manager.from table
+          manager.order :foo
+          manager.to_sql.must_be_like %{ SELECT * FROM "users" ORDER BY foo }
+        end
+      end
+
+      describe 'group' do
+        it 'takes a symbol' do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.from table
+          manager.group :foo
+          manager.to_sql.must_be_like %{ SELECT FROM "users" GROUP BY foo }
+        end
+      end
+
+      describe 'as' do
+        it 'makes an AS node by grouping the AST' do
+          manager = Arel::SelectManager.new
+          as = manager.as(Arel.sql('foo'))
+          assert_kind_of Arel::Nodes::Grouping, as.left
+          assert_equal manager.ast, as.left.expr
+          assert_equal 'foo', as.right
+        end
+
+        it 'converts right to SqlLiteral if a string' do
+          manager = Arel::SelectManager.new
+          as = manager.as('foo')
+          assert_kind_of Arel::Nodes::SqlLiteral, as.right
+        end
+
+        it 'can make a subselect' do
+          manager = Arel::SelectManager.new
+          manager.project Arel.star
+          manager.from Arel.sql('zomg')
+          as = manager.as(Arel.sql('foo'))
+
+          manager = Arel::SelectManager.new
+          manager.project Arel.sql('name')
+          manager.from as
+          manager.to_sql.must_be_like "SELECT name FROM (SELECT * FROM zomg) foo"
+        end
+      end
+
+      describe 'from' do
+        it 'ignores strings when table of same name exists' do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+
+          manager.from table
+          manager.from 'users'
+          manager.project table['id']
+          manager.to_sql.must_be_like 'SELECT "users"."id" FROM users'
+        end
+
+        it 'should support any ast' do
+          table   = Table.new :users
+          manager1 = Arel::SelectManager.new
+
+          manager2 = Arel::SelectManager.new
+          manager2.project(Arel.sql('*'))
+          manager2.from table
+
+          manager1.project Arel.sql('lol')
+          as = manager2.as Arel.sql('omg')
+          manager1.from(as)
+
+          manager1.to_sql.must_be_like %{
+            SELECT lol FROM (SELECT * FROM "users") omg
+          }
+        end
+      end
+
+      describe 'having' do
+        it 'converts strings to SQLLiterals' do
+          table   = Table.new :users
+          mgr = table.from
+          mgr.having Arel.sql('foo')
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo }
+        end
+
+        it 'can have multiple items specified separately' do
+          table = Table.new :users
+          mgr = table.from
+          mgr.having Arel.sql('foo')
+          mgr.having Arel.sql('bar')
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo AND bar }
+        end
+
+        it 'can receive any node' do
+          table = Table.new :users
+          mgr = table.from
+          mgr.having Arel::Nodes::And.new([Arel.sql('foo'), Arel.sql('bar')])
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo AND bar }
+        end
+      end
+
+      describe 'on' do
+        it 'converts to sqlliterals' do
+          table = Table.new :users
+          right = table.alias
+          mgr   = table.from
+          mgr.join(right).on("omg")
+          mgr.to_sql.must_be_like %{ SELECT  FROM "users" INNER JOIN "users" "users_2" ON omg }
+        end
+
+        it 'converts to sqlliterals with multiple items' do
+          table = Table.new :users
+          right = table.alias
+          mgr   = table.from
+          mgr.join(right).on("omg", "123")
+          mgr.to_sql.must_be_like %{ SELECT  FROM "users" INNER JOIN "users" "users_2" ON omg AND 123 }
+        end
+      end
+    end
+
+    describe 'clone' do
+      it 'creates new cores' do
+        table   = Table.new :users, :as => 'foo'
+        mgr = table.from
+        m2 = mgr.clone
+        m2.project "foo"
+        mgr.to_sql.wont_equal m2.to_sql
+      end
+
+      it 'makes updates to the correct copy' do
+        table   = Table.new :users, :as => 'foo'
+        mgr = table.from
+        m2 = mgr.clone
+        m3 = m2.clone
+        m2.project "foo"
+        mgr.to_sql.wont_equal m2.to_sql
+        m3.to_sql.must_equal mgr.to_sql
+      end
+    end
+
+    describe 'initialize' do
+      it 'uses alias in sql' do
+        table   = Table.new :users, :as => 'foo'
+        mgr = table.from
+        mgr.skip 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" "foo" OFFSET 10 }
+      end
+    end
+
+    describe 'skip' do
+      it 'should add an offset' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.skip 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+
+      it 'should chain' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.skip(10).to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+    end
+
+    describe 'offset' do
+      it 'should add an offset' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+
+      it 'should remove an offset' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+
+        mgr.offset = nil
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" }
+      end
+
+      it 'should return the offset' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        assert_equal 10, mgr.offset
+      end
+    end
+
+    describe 'exists' do
+      it 'should create an exists clause' do
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.project Nodes::SqlLiteral.new '*'
+        m2 = Arel::SelectManager.new
+        m2.project manager.exists
+        m2.to_sql.must_be_like %{ SELECT EXISTS (#{manager.to_sql}) }
+      end
+
+      it 'can be aliased' do
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.project Nodes::SqlLiteral.new '*'
+        m2 = Arel::SelectManager.new
+        m2.project manager.exists.as('foo')
+        m2.to_sql.must_be_like %{ SELECT EXISTS (#{manager.to_sql}) AS foo }
+      end
+    end
+
+    describe 'union' do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].lt(18))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].gt(99))
+
+
+      end
+
+      it 'should union two managers' do
+        # FIXME should this union "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.union @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" < 18 UNION SELECT * FROM "users"  WHERE "users"."age" > 99 )
+        }
+      end
+
+      it 'should union all' do
+        node = @m1.union :all, @m2
+
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" < 18 UNION ALL SELECT * FROM "users"  WHERE "users"."age" > 99 )
+        }
+      end
+
+    end
+
+    describe 'intersect' do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].gt(18))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].lt(99))
+
+
+      end
+
+      it 'should interect two managers' do
+        # FIXME should this intersect "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.intersect @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" > 18 INTERSECT SELECT * FROM "users"  WHERE "users"."age" < 99 )
+        }
+      end
+
+    end
+
+    describe 'except' do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].between(18..60))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].between(40..99))
+      end
+
+      it 'should except two managers' do
+        # FIXME should this except "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.except @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" BETWEEN 18 AND 60 EXCEPT SELECT * FROM "users"  WHERE "users"."age" BETWEEN 40 AND 99 )
+        }
+      end
+
+    end
+
+    describe 'with' do
+      it 'should support basic WITH' do
+        users          = Table.new(:users)
+        users_top      = Table.new(:users_top)
+        comments       = Table.new(:comments)
+
+        top            = users.project(users[:id]).where(users[:karma].gt(100))
+        users_as       = Arel::Nodes::As.new(users_top, top)
+        select_manager = comments.project(Arel.star).with(users_as)
+                          .where(comments[:author_id].in(users_top.project(users_top[:id])))
+
+        select_manager.to_sql.must_be_like %{
+          WITH "users_top" AS (SELECT "users"."id" FROM "users" WHERE "users"."karma" > 100) SELECT * FROM "comments" WHERE "comments"."author_id" IN (SELECT "users_top"."id" FROM "users_top")
+        }
+      end
+
+      it "should support WITH RECURSIVE" do
+        comments           = Table.new(:comments)
+        comments_id        = comments[:id]
+        comments_parent_id = comments[:parent_id]
+
+        replies            = Table.new(:replies)
+        replies_id         = replies[:id]
+
+        recursive_term = Arel::SelectManager.new
+        recursive_term.from(comments).project(comments_id, comments_parent_id).where(comments_id.eq 42)
+
+        non_recursive_term = Arel::SelectManager.new
+        non_recursive_term.from(comments).project(comments_id, comments_parent_id).join(replies).on(comments_parent_id.eq replies_id)
+
+        union = recursive_term.union(non_recursive_term)
+
+        as_statement = Arel::Nodes::As.new replies, union
+
+        manager = Arel::SelectManager.new
+        manager.with(:recursive, as_statement).from(replies).project(Arel.star)
+
+        sql = manager.to_sql
+        sql.must_be_like %{
+          WITH RECURSIVE "replies" AS (
+              SELECT "comments"."id", "comments"."parent_id" FROM "comments" WHERE "comments"."id" = 42
+            UNION
+              SELECT "comments"."id", "comments"."parent_id" FROM "comments" INNER JOIN "replies" ON "comments"."parent_id" = "replies"."id"
+          )
+          SELECT * FROM "replies"
+        }
+      end
+    end
+
+    describe 'ast' do
+      it 'should return the ast' do
+        table   = Table.new :users
+        mgr = table.from
+        assert mgr.ast
+      end
+
+      it 'should allow orders to work when the ast is grepped' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.project Arel.sql '*'
+        mgr.from table
+        mgr.orders << Arel::Nodes::Ascending.new(Arel.sql('foo'))
+        mgr.ast.grep(Arel::Nodes::OuterJoin)
+        mgr.to_sql.must_be_like %{ SELECT * FROM "users" ORDER BY foo ASC }
+      end
+    end
+
+    describe 'taken' do
+      it 'should return limit' do
+        manager = Arel::SelectManager.new
+        manager.take 10
+        manager.taken.must_equal 10
+      end
+    end
+
+    describe 'lock' do
+      # This should fail on other databases
+      it 'adds a lock node' do
+        table   = Table.new :users
+        mgr = table.from
+        mgr.lock.to_sql.must_be_like %{ SELECT FROM "users" FOR UPDATE }
+      end
+    end
+
+    describe 'orders' do
+      it 'returns order clauses' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        order = table[:id]
+        manager.order table[:id]
+        manager.orders.must_equal [order]
+      end
+    end
+
+    describe 'order' do
+      it 'generates order clauses' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new '*'
+        manager.from table
+        manager.order table[:id]
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id"
+        }
+      end
+
+      # FIXME: I would like to deprecate this
+      it 'takes *args' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new '*'
+        manager.from table
+        manager.order table[:id], table[:name]
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id", "users"."name"
+        }
+      end
+
+      it 'chains' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.order(table[:id]).must_equal manager
+      end
+
+      it 'has order attributes' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new '*'
+        manager.from table
+        manager.order table[:id].desc
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id" DESC
+        }
+      end
+    end
+
+    describe 'on' do
+      it 'takes two params' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(predicate, predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id" AND
+               "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'takes three params' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(
+          predicate,
+          predicate,
+          left[:name].eq(right[:name])
+        )
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id" AND
+               "users"."id" = "users_2"."id" AND
+               "users"."name" = "users_2"."name"
+        }
+      end
+    end
+
+    it 'should hand back froms' do
+      relation = Arel::SelectManager.new
+      assert_equal [], relation.froms
+    end
+
+    it 'should create and nodes' do
+      relation = Arel::SelectManager.new
+      children = ['foo', 'bar', 'baz']
+      clause = relation.create_and children
+      assert_kind_of Arel::Nodes::And, clause
+      assert_equal children, clause.children
+    end
+
+    it 'should create insert managers' do
+      relation = Arel::SelectManager.new
+      insert = relation.create_insert
+      assert_kind_of Arel::InsertManager, insert
+    end
+
+    it 'should create join nodes' do
+      relation = Arel::SelectManager.new
+      join = relation.create_join 'foo', 'bar'
+      assert_kind_of Arel::Nodes::InnerJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a full outer join klass' do
+      relation = Arel::SelectManager.new
+      join = relation.create_join 'foo', 'bar', Arel::Nodes::FullOuterJoin
+      assert_kind_of Arel::Nodes::FullOuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a outer join klass' do
+      relation = Arel::SelectManager.new
+      join = relation.create_join 'foo', 'bar', Arel::Nodes::OuterJoin
+      assert_kind_of Arel::Nodes::OuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a right outer join klass' do
+      relation = Arel::SelectManager.new
+      join = relation.create_join 'foo', 'bar', Arel::Nodes::RightOuterJoin
+      assert_kind_of Arel::Nodes::RightOuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    describe 'join' do
+      it 'responds to join' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'takes a class' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::OuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'takes the full outer join class' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::FullOuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             FULL OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'takes the right outer join class' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::RightOuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             RIGHT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'noops on nil' do
+        manager   = Arel::SelectManager.new
+        manager.join(nil).must_equal manager
+      end
+
+      it 'raises EmptyJoinError on empty' do
+        left      = Table.new :users
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        assert_raises(EmptyJoinError) do
+          manager.join("")
+        end
+      end
+    end
+
+    describe 'outer join' do
+      it 'responds to join' do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.outer_join(right).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'noops on nil' do
+        manager   = Arel::SelectManager.new
+        manager.outer_join(nil).must_equal manager
+      end
+    end
+
+    describe 'joins' do
+
+      it 'returns inner join sql' do
+        table   = Table.new :users
+        aliaz   = table.alias
+        manager = Arel::SelectManager.new
+        manager.from Nodes::InnerJoin.new(aliaz, table[:id].eq(aliaz[:id]))
+        assert_match 'INNER JOIN "users" "users_2" "users"."id" = "users_2"."id"',
+                     manager.to_sql
+      end
+
+      it 'returns outer join sql' do
+        table   = Table.new :users
+        aliaz   = table.alias
+        manager = Arel::SelectManager.new
+        manager.from Nodes::OuterJoin.new(aliaz, table[:id].eq(aliaz[:id]))
+        assert_match 'LEFT OUTER JOIN "users" "users_2" "users"."id" = "users_2"."id"',
+                     manager.to_sql
+      end
+
+      it 'can have a non-table alias as relation name' do
+        users    = Table.new :users
+        comments = Table.new :comments
+
+        counts = comments.from.
+          group(comments[:user_id]).
+          project(
+            comments[:user_id].as("user_id"),
+            comments[:user_id].count.as("count")
+          ).as("counts")
+
+        joins = users.join(counts).on(counts[:user_id].eq(10))
+        joins.to_sql.must_be_like  %{
+          SELECT FROM "users" INNER JOIN (SELECT "comments"."user_id" AS user_id, COUNT("comments"."user_id") AS count FROM "comments" GROUP BY "comments"."user_id") counts ON counts."user_id" = 10
+        }
+      end
+
+      it "joins itself" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+
+        mgr = left.join(right)
+        mgr.project Nodes::SqlLiteral.new('*')
+        mgr.on(predicate).must_equal mgr
+
+        mgr.to_sql.must_be_like %{
+           SELECT * FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it 'returns string join sql' do
+        manager = Arel::SelectManager.new
+        manager.from Nodes::StringJoin.new(Nodes.build_quoted('hello'))
+        assert_match "'hello'", manager.to_sql
+      end
+    end
+
+    describe 'group' do
+      it 'takes an attribute' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group table[:id]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id"
+        }
+      end
+
+      it 'chains' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.group(table[:id]).must_equal manager
+      end
+
+      it 'takes multiple args' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group table[:id], table[:name]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id", "users"."name"
+        }
+      end
+
+      # FIXME: backwards compat
+      it 'makes strings literals' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group 'foo'
+        manager.to_sql.must_be_like %{ SELECT FROM "users" GROUP BY foo }
+      end
+    end
+
+    describe 'window definition' do
+      it 'can be empty' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window')
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS ()
+        }
+      end
+
+      it 'takes an order' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').order(table['foo'].asc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ORDER BY "users"."foo" ASC)
+        }
+      end
+
+      it 'takes an order with multiple columns' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').order(table['foo'].asc, table['bar'].desc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ORDER BY "users"."foo" ASC, "users"."bar" DESC)
+        }
+      end
+
+      it 'takes a partition' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').partition(table['bar'])
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."bar")
+        }
+      end
+
+      it 'takes a partition and an order' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').partition(table['foo']).order(table['foo'].asc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."foo"
+            ORDER BY "users"."foo" ASC)
+        }
+      end
+
+      it 'takes a partition with multiple columns' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').partition(table['bar'], table['baz'])
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."bar", "users"."baz")
+        }
+      end
+
+      it 'takes a rows frame, unbounded preceding' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').rows(Arel::Nodes::Preceding.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS UNBOUNDED PRECEDING)
+        }
+      end
+
+      it 'takes a rows frame, bounded preceding' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').rows(Arel::Nodes::Preceding.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS 5 PRECEDING)
+        }
+      end
+
+      it 'takes a rows frame, unbounded following' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').rows(Arel::Nodes::Following.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS UNBOUNDED FOLLOWING)
+        }
+      end
+
+      it 'takes a rows frame, bounded following' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').rows(Arel::Nodes::Following.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS 5 FOLLOWING)
+        }
+      end
+
+      it 'takes a rows frame, current row' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').rows(Arel::Nodes::CurrentRow.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS CURRENT ROW)
+        }
+      end
+
+      it 'takes a rows frame, between two delimiters' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        window = manager.window('a_window')
+        window.frame(
+          Arel::Nodes::Between.new(
+            window.rows,
+            Nodes::And.new([
+              Arel::Nodes::Preceding.new,
+              Arel::Nodes::CurrentRow.new
+            ])))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
+        }
+      end
+
+      it 'takes a range frame, unbounded preceding' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').range(Arel::Nodes::Preceding.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE UNBOUNDED PRECEDING)
+        }
+      end
+
+      it 'takes a range frame, bounded preceding' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').range(Arel::Nodes::Preceding.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE 5 PRECEDING)
+        }
+      end
+
+      it 'takes a range frame, unbounded following' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').range(Arel::Nodes::Following.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE UNBOUNDED FOLLOWING)
+        }
+      end
+
+      it 'takes a range frame, bounded following' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').range(Arel::Nodes::Following.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE 5 FOLLOWING)
+        }
+      end
+
+      it 'takes a range frame, current row' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window('a_window').range(Arel::Nodes::CurrentRow.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE CURRENT ROW)
+        }
+      end
+
+      it 'takes a range frame, between two delimiters' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        window = manager.window('a_window')
+        window.frame(
+          Arel::Nodes::Between.new(
+            window.range,
+            Nodes::And.new([
+              Arel::Nodes::Preceding.new,
+              Arel::Nodes::CurrentRow.new
+            ])))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
+        }
+      end
+    end
+
+    describe 'delete' do
+      it "copies from" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_delete
+
+        stmt.to_sql.must_be_like %{ DELETE FROM "users" }
+      end
+
+      it "copies where" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        stmt = manager.compile_delete
+
+        stmt.to_sql.must_be_like %{
+          DELETE FROM "users" WHERE "users"."id" = 10
+        }
+      end
+    end
+
+    describe 'where_sql' do
+      it 'gives me back the where sql' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 }
+      end
+
+      it 'joins wheres with AND' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where table[:id].eq 11
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 AND "users"."id" = 11}
+      end
+
+      it 'handles database specific statements' do
+        old_visitor = Table.engine.connection.visitor
+        Table.engine.connection.visitor = Visitors::PostgreSQL.new Table.engine.connection
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where table[:name].matches 'foo%'
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 AND "users"."name" ILIKE 'foo%' }
+        Table.engine.connection.visitor = old_visitor
+      end
+
+      it 'returns nil when there are no wheres' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where_sql.must_be_nil
+      end
+    end
+
+    describe 'update' do
+
+      it 'creates an update statement' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_update({table[:id] => 1}, Arel::Attributes::Attribute.new(table, 'id'))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1
+        }
+      end
+
+      it 'takes a string' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_update(Nodes::SqlLiteral.new('foo = bar'), Arel::Attributes::Attribute.new(table, 'id'))
+
+        stmt.to_sql.must_be_like %{ UPDATE "users" SET foo = bar }
+      end
+
+      it 'copies limits' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.take 1
+        stmt = manager.compile_update(Nodes::SqlLiteral.new('foo = bar'), Arel::Attributes::Attribute.new(table, 'id'))
+        stmt.key = table['id']
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET foo = bar
+          WHERE "users"."id" IN (SELECT "users"."id" FROM "users" LIMIT 1)
+        }
+      end
+
+      it 'copies order' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.order :foo
+        stmt = manager.compile_update(Nodes::SqlLiteral.new('foo = bar'), Arel::Attributes::Attribute.new(table, 'id'))
+        stmt.key = table['id']
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET foo = bar
+          WHERE "users"."id" IN (SELECT "users"."id" FROM "users" ORDER BY foo)
+        }
+      end
+
+      it 'copies where clauses' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.where table[:id].eq 10
+        manager.from table
+        stmt = manager.compile_update({table[:id] => 1}, Arel::Attributes::Attribute.new(table, 'id'))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1 WHERE "users"."id" = 10
+        }
+      end
+
+      it 'copies where clauses when nesting is triggered' do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.where table[:foo].eq 10
+        manager.take 42
+        manager.from table
+        stmt = manager.compile_update({table[:id] => 1}, Arel::Attributes::Attribute.new(table, 'id'))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1 WHERE "users"."id" IN (SELECT "users"."id" FROM "users" WHERE "users"."foo" = 10 LIMIT 42)
+        }
+      end
+
+    end
+
+    describe 'project' do
+      it "takes sql literals" do
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new '*'
+        manager.to_sql.must_be_like %{ SELECT * }
+      end
+
+      it 'takes multiple args' do
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new('foo'),
+          Nodes::SqlLiteral.new('bar')
+        manager.to_sql.must_be_like %{ SELECT foo, bar }
+      end
+
+      it 'takes strings' do
+        manager = Arel::SelectManager.new
+        manager.project '*'
+        manager.to_sql.must_be_like %{ SELECT * }
+      end
+
+    end
+
+    describe 'projections' do
+      it 'reads projections' do
+        manager = Arel::SelectManager.new
+        manager.project Arel.sql('foo'), Arel.sql('bar')
+        manager.projections.must_equal [Arel.sql('foo'), Arel.sql('bar')]
+      end
+    end
+
+    describe 'projections=' do
+      it 'overwrites projections' do
+        manager = Arel::SelectManager.new
+        manager.project Arel.sql('foo')
+        manager.projections = [Arel.sql('bar')]
+        manager.to_sql.must_be_like %{ SELECT bar }
+      end
+    end
+
+    describe 'take' do
+      it "knows take" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table['id'])
+        manager.where(table['id'].eq(1))
+        manager.take 1
+
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+          LIMIT 1
+        }
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        manager.take(1).must_equal manager
+      end
+
+      it 'removes LIMIT when nil is passed' do
+        manager = Arel::SelectManager.new
+        manager.limit = 10
+        assert_match('LIMIT', manager.to_sql)
+
+        manager.limit = nil
+        refute_match('LIMIT', manager.to_sql)
+      end
+    end
+
+    describe 'where' do
+      it "knows where" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table['id'])
+        manager.where(table['id'].eq(1))
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+        }
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table)
+        manager.project(table['id']).where(table['id'].eq 1).must_equal manager
+      end
+    end
+
+    describe 'from' do
+      it "makes sql" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+
+        manager.from table
+        manager.project table['id']
+        manager.to_sql.must_be_like 'SELECT "users"."id" FROM "users"'
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table['id']).must_equal manager
+        manager.to_sql.must_be_like 'SELECT "users"."id" FROM "users"'
+      end
+    end
+
+    describe 'source' do
+      it 'returns the join source of the select core' do
+        manager = Arel::SelectManager.new
+        manager.source.must_equal manager.ast.cores.last.source
+      end
+    end
+
+    describe 'distinct' do
+      it 'sets the quantifier' do
+        manager = Arel::SelectManager.new
+
+        manager.distinct
+        manager.ast.cores.last.set_quantifier.class.must_equal Arel::Nodes::Distinct
+
+        manager.distinct(false)
+        manager.ast.cores.last.set_quantifier.must_be_nil
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        manager.distinct.must_equal manager
+        manager.distinct(false).must_equal manager
+      end
+    end
+
+    describe 'distinct_on' do
+      it 'sets the quantifier' do
+        manager = Arel::SelectManager.new
+        table = Table.new :users
+
+        manager.distinct_on(table['id'])
+        manager.ast.cores.last.set_quantifier.must_equal Arel::Nodes::DistinctOn.new(table['id'])
+
+        manager.distinct_on(false)
+        manager.ast.cores.last.set_quantifier.must_be_nil
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        table = Table.new :users
+
+        manager.distinct_on(table['id']).must_equal manager
+        manager.distinct_on(false).must_equal manager
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/support/fake_record.rb b/activerecord/test/cases/arel/support/fake_record.rb
new file mode 100644
index 0000000000..75ac1e072f
--- /dev/null
+++ b/activerecord/test/cases/arel/support/fake_record.rb
@@ -0,0 +1,129 @@
+# frozen_string_literal: true
+
+require 'date'
+module FakeRecord
+  class Column < Struct.new(:name, :type)
+  end
+
+  class Connection
+    attr_reader :tables
+    attr_accessor :visitor
+
+    def initialize(visitor = nil)
+      @tables = %w{ users photos developers products}
+      @columns = {
+        'users' => [
+          Column.new('id', :integer),
+          Column.new('name', :string),
+          Column.new('bool', :boolean),
+          Column.new('created_at', :date)
+        ],
+        'products' => [
+          Column.new('id', :integer),
+          Column.new('price', :decimal)
+        ]
+      }
+      @columns_hash = {
+        'users' => Hash[@columns['users'].map { |x| [x.name, x] }],
+        'products' => Hash[@columns['products'].map { |x| [x.name, x] }]
+      }
+      @primary_keys = {
+        'users' => 'id',
+        'products' => 'id'
+      }
+      @visitor = visitor
+    end
+
+    def columns_hash table_name
+      @columns_hash[table_name]
+    end
+
+    def primary_key name
+      @primary_keys[name.to_s]
+    end
+
+    def data_source_exists? name
+      @tables.include? name.to_s
+    end
+
+    def columns name, message = nil
+      @columns[name.to_s]
+    end
+
+    def quote_table_name name
+      "\"#{name.to_s}\""
+    end
+
+    def quote_column_name name
+      "\"#{name.to_s}\""
+    end
+
+    def schema_cache
+      self
+    end
+
+    def quote thing
+      case thing
+      when DateTime
+        "'#{thing.strftime("%Y-%m-%d %H:%M:%S")}'"
+      when Date
+        "'#{thing.strftime("%Y-%m-%d")}'"
+      when true
+        "'t'"
+      when false
+        "'f'"
+      when nil
+        'NULL'
+      when Numeric
+        thing
+      else
+        "'#{thing.to_s.gsub("'", "\\\\'")}'"
+      end
+    end
+  end
+
+  class ConnectionPool
+    class Spec < Struct.new(:config)
+    end
+
+    attr_reader :spec, :connection
+
+    def initialize
+      @spec = Spec.new(:adapter => 'america')
+      @connection = Connection.new
+      @connection.visitor = Arel::Visitors::ToSql.new(connection)
+    end
+
+    def with_connection
+      yield connection
+    end
+
+    def table_exists? name
+      connection.tables.include? name.to_s
+    end
+
+    def columns_hash
+      connection.columns_hash
+    end
+
+    def schema_cache
+      connection
+    end
+
+    def quote thing
+      connection.quote thing
+    end
+  end
+
+  class Base
+    attr_accessor :connection_pool
+
+    def initialize
+      @connection_pool = ConnectionPool.new
+    end
+
+    def connection
+      connection_pool.connection
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/table_test.rb b/activerecord/test/cases/arel/table_test.rb
new file mode 100644
index 0000000000..ccb3ab302f
--- /dev/null
+++ b/activerecord/test/cases/arel/table_test.rb
@@ -0,0 +1,215 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  class TableTest < Arel::Spec
+    before do
+      @relation = Table.new(:users)
+    end
+
+    it 'should create join nodes' do
+      join = @relation.create_string_join 'foo'
+      assert_kind_of Arel::Nodes::StringJoin, join
+      assert_equal 'foo', join.left
+    end
+
+    it 'should create join nodes' do
+      join = @relation.create_join 'foo', 'bar'
+      assert_kind_of Arel::Nodes::InnerJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a klass' do
+      join = @relation.create_join 'foo', 'bar', Arel::Nodes::FullOuterJoin
+      assert_kind_of Arel::Nodes::FullOuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a klass' do
+      join = @relation.create_join 'foo', 'bar', Arel::Nodes::OuterJoin
+      assert_kind_of Arel::Nodes::OuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should create join nodes with a klass' do
+      join = @relation.create_join 'foo', 'bar', Arel::Nodes::RightOuterJoin
+      assert_kind_of Arel::Nodes::RightOuterJoin, join
+      assert_equal 'foo', join.left
+      assert_equal 'bar', join.right
+    end
+
+    it 'should return an insert manager' do
+      im = @relation.compile_insert 'VALUES(NULL)'
+      assert_kind_of Arel::InsertManager, im
+      im.into Table.new(:users)
+      assert_equal "INSERT INTO \"users\" VALUES(NULL)", im.to_sql
+    end
+
+    describe 'skip' do
+      it 'should add an offset' do
+        sm = @relation.skip 2
+        sm.to_sql.must_be_like "SELECT FROM \"users\" OFFSET 2"
+      end
+    end
+
+    describe 'having' do
+      it 'adds a having clause' do
+        mgr = @relation.having @relation[:id].eq(10)
+        mgr.to_sql.must_be_like %{
+         SELECT FROM "users" HAVING "users"."id" = 10
+        }
+      end
+    end
+
+    describe 'backwards compat' do
+      describe 'join' do
+        it 'noops on nil' do
+          mgr = @relation.join nil
+
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" }
+        end
+
+        it 'raises EmptyJoinError on empty' do
+          assert_raises(EmptyJoinError) do
+            @relation.join ""
+          end
+        end
+
+        it 'takes a second argument for join type' do
+          right     = @relation.alias
+          predicate = @relation[:id].eq(right[:id])
+          mgr = @relation.join(right, Nodes::OuterJoin).on(predicate)
+
+          mgr.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+          }
+        end
+      end
+
+      describe 'join' do
+        it 'creates an outer join' do
+          right     = @relation.alias
+          predicate = @relation[:id].eq(right[:id])
+          mgr = @relation.outer_join(right).on(predicate)
+
+          mgr.to_sql.must_be_like %{
+            SELECT FROM "users"
+              LEFT OUTER JOIN "users" "users_2"
+                ON "users"."id" = "users_2"."id"
+          }
+        end
+      end
+    end
+
+    describe 'group' do
+      it 'should create a group' do
+        manager = @relation.group @relation[:id]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id"
+        }
+      end
+    end
+
+    describe 'alias' do
+      it 'should create a node that proxies to a table' do
+        node = @relation.alias
+        node.name.must_equal 'users_2'
+        node[:id].relation.must_equal node
+      end
+    end
+
+    describe 'new' do
+      it 'should accept a hash' do
+        rel = Table.new :users, :as => 'foo'
+        rel.table_alias.must_equal 'foo'
+      end
+
+      it 'ignores as if it equals name' do
+        rel = Table.new :users, :as => 'users'
+        rel.table_alias.must_be_nil
+      end
+    end
+
+    describe 'order' do
+      it "should take an order" do
+        manager = @relation.order "foo"
+        manager.to_sql.must_be_like %{ SELECT FROM "users" ORDER BY foo }
+      end
+    end
+
+    describe 'take' do
+      it "should add a limit" do
+        manager = @relation.take 1
+        manager.project Nodes::SqlLiteral.new '*'
+        manager.to_sql.must_be_like %{ SELECT * FROM "users" LIMIT 1 }
+      end
+    end
+
+    describe 'project' do
+      it 'can project' do
+        manager = @relation.project Nodes::SqlLiteral.new '*'
+        manager.to_sql.must_be_like %{ SELECT * FROM "users" }
+      end
+
+      it 'takes multiple parameters' do
+        manager = @relation.project Nodes::SqlLiteral.new('*'), Nodes::SqlLiteral.new('*')
+        manager.to_sql.must_be_like %{ SELECT *, * FROM "users" }
+      end
+    end
+
+    describe 'where' do
+      it "returns a tree manager" do
+        manager = @relation.where @relation[:id].eq 1
+        manager.project @relation[:id]
+        manager.must_be_kind_of TreeManager
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+        }
+      end
+    end
+
+    it "should have a name" do
+      @relation.name.must_equal 'users'
+    end
+
+    it "should have a table name" do
+      @relation.table_name.must_equal 'users'
+    end
+
+    describe '[]' do
+      describe 'when given a Symbol' do
+        it "manufactures an attribute if the symbol names an attribute within the relation" do
+          column = @relation[:id]
+          column.name.must_equal :id
+        end
+      end
+    end
+
+    describe 'equality' do
+      it 'is equal with equal ivars' do
+        relation1 = Table.new(:users)
+        relation1.table_alias = 'zomg'
+        relation2 = Table.new(:users)
+        relation2.table_alias = 'zomg'
+        array = [relation1, relation2]
+        assert_equal 1, array.uniq.size
+      end
+
+      it 'is not equal with different ivars' do
+        relation1 = Table.new(:users)
+        relation1.table_alias = 'zomg'
+        relation2 = Table.new(:users)
+        relation2.table_alias = 'zomg2'
+        array = [relation1, relation2]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/update_manager_test.rb b/activerecord/test/cases/arel/update_manager_test.rb
new file mode 100644
index 0000000000..91118c5e9f
--- /dev/null
+++ b/activerecord/test/cases/arel/update_manager_test.rb
@@ -0,0 +1,125 @@
+# frozen_string_literal: true
+require_relative 'helper'
+
+module Arel
+  class UpdateManagerTest < Arel::Spec
+    describe 'new' do
+      it 'takes an engine' do
+        Arel::UpdateManager.new
+      end
+    end
+
+    it "should not quote sql literals" do
+      table = Table.new(:users)
+      um = Arel::UpdateManager.new
+      um.table table
+      um.set [[table[:name], Arel::Nodes::BindParam.new(1)]]
+      um.to_sql.must_be_like %{ UPDATE "users" SET "name" =  ? }
+    end
+
+    it 'handles limit properly' do
+      table = Table.new(:users)
+      um = Arel::UpdateManager.new
+      um.key = 'id'
+      um.take 10
+      um.table table
+      um.set [[table[:name], nil]]
+      assert_match(/LIMIT 10/, um.to_sql)
+    end
+
+    describe 'set' do
+      it "updates with null" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set [[table[:name], nil]]
+        um.to_sql.must_be_like %{ UPDATE "users" SET "name" =  NULL }
+      end
+
+      it 'takes a string' do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set Nodes::SqlLiteral.new "foo = bar"
+        um.to_sql.must_be_like %{ UPDATE "users" SET foo = bar }
+      end
+
+      it 'takes a list of lists' do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set [[table[:id], 1], [table[:name], 'hello']]
+        um.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1, "name" =  'hello'
+        }
+      end
+
+      it 'chains' do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.set([[table[:id], 1], [table[:name], 'hello']]).must_equal um
+      end
+    end
+
+    describe 'table' do
+      it 'generates an update statement' do
+        um = Arel::UpdateManager.new
+        um.table Table.new(:users)
+        um.to_sql.must_be_like %{ UPDATE "users" }
+      end
+
+      it 'chains' do
+        um = Arel::UpdateManager.new
+        um.table(Table.new(:users)).must_equal um
+      end
+
+      it 'generates an update statement with joins' do
+        um = Arel::UpdateManager.new
+
+        table = Table.new(:users)
+        join_source = Arel::Nodes::JoinSource.new(
+          table,
+          [table.create_join(Table.new(:posts))]
+        )
+
+        um.table join_source
+        um.to_sql.must_be_like %{ UPDATE "users" INNER JOIN "posts" }
+      end
+    end
+
+    describe 'where' do
+      it 'generates a where clause' do
+        table = Table.new :users
+        um = Arel::UpdateManager.new
+        um.table table
+        um.where table[:id].eq(1)
+        um.to_sql.must_be_like %{
+          UPDATE "users" WHERE "users"."id" = 1
+        }
+      end
+
+      it 'chains' do
+        table = Table.new :users
+        um = Arel::UpdateManager.new
+        um.table table
+        um.where(table[:id].eq(1)).must_equal um
+      end
+    end
+
+    describe 'key' do
+      before do
+        @table = Table.new :users
+        @um = Arel::UpdateManager.new
+        @um.key = @table[:foo]
+      end
+
+      it 'can be set' do
+        @um.ast.key.must_equal @table[:foo]
+      end
+
+      it 'can be accessed' do
+        @um.key.must_equal @table[:foo]
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/depth_first_test.rb b/activerecord/test/cases/arel/visitors/depth_first_test.rb
new file mode 100644
index 0000000000..b841d119d2
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/depth_first_test.rb
@@ -0,0 +1,270 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class TestDepthFirst < Arel::Test
+      Collector = Struct.new(:calls) do
+        def call object
+          calls << object
+        end
+      end
+
+      def setup
+        @collector = Collector.new []
+        @visitor = Visitors::DepthFirst.new @collector
+      end
+
+      def test_raises_with_object
+        assert_raises(TypeError) do
+          @visitor.accept(Object.new)
+        end
+      end
+
+
+      # unary ops
+      [
+        Arel::Nodes::Not,
+        Arel::Nodes::Group,
+        Arel::Nodes::On,
+        Arel::Nodes::Grouping,
+        Arel::Nodes::Offset,
+        Arel::Nodes::Ordering,
+        Arel::Nodes::StringJoin,
+        Arel::Nodes::UnqualifiedColumn,
+        Arel::Nodes::Top,
+        Arel::Nodes::Limit,
+        Arel::Nodes::Else,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a)
+          @visitor.accept op
+          assert_equal [:a, op], @collector.calls
+        end
+      end
+
+      # functions
+      [
+        Arel::Nodes::Exists,
+        Arel::Nodes::Avg,
+        Arel::Nodes::Min,
+        Arel::Nodes::Max,
+        Arel::Nodes::Sum,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          func = klass.new(:a, "b")
+          @visitor.accept func
+          assert_equal [:a, "b", false, func], @collector.calls
+        end
+      end
+
+      def test_named_function
+        func = Arel::Nodes::NamedFunction.new(:a, :b, "c")
+        @visitor.accept func
+        assert_equal [:a, :b, false, "c", func], @collector.calls
+      end
+
+      def test_lock
+        lock = Nodes::Lock.new true
+        @visitor.accept lock
+        assert_equal [lock], @collector.calls
+      end
+
+      def test_count
+        count = Nodes::Count.new :a, :b, "c"
+        @visitor.accept count
+        assert_equal [:a, "c", :b, count], @collector.calls
+      end
+
+      def test_inner_join
+        join = Nodes::InnerJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_full_outer_join
+        join = Nodes::FullOuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_outer_join
+        join = Nodes::OuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_right_outer_join
+        join = Nodes::RightOuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      [
+        Arel::Nodes::Assignment,
+        Arel::Nodes::Between,
+        Arel::Nodes::Concat,
+        Arel::Nodes::DoesNotMatch,
+        Arel::Nodes::Equality,
+        Arel::Nodes::GreaterThan,
+        Arel::Nodes::GreaterThanOrEqual,
+        Arel::Nodes::In,
+        Arel::Nodes::LessThan,
+        Arel::Nodes::LessThanOrEqual,
+        Arel::Nodes::Matches,
+        Arel::Nodes::NotEqual,
+        Arel::Nodes::NotIn,
+        Arel::Nodes::Or,
+        Arel::Nodes::TableAlias,
+        Arel::Nodes::Values,
+        Arel::Nodes::As,
+        Arel::Nodes::DeleteStatement,
+        Arel::Nodes::JoinSource,
+        Arel::Nodes::When,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary
+          assert_equal [:a, :b, binary], @collector.calls
+        end
+      end
+
+      def test_Arel_Nodes_InfixOperation
+        binary = Arel::Nodes::InfixOperation.new(:o, :a, :b)
+        @visitor.accept binary
+        assert_equal [:a, :b, binary], @collector.calls
+      end
+
+      # N-ary
+      [
+        Arel::Nodes::And,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new([:a, :b, :c])
+          @visitor.accept binary
+          assert_equal [:a, :b, :c, binary], @collector.calls
+        end
+      end
+
+      [
+        Arel::Attributes::Integer,
+        Arel::Attributes::Float,
+        Arel::Attributes::String,
+        Arel::Attributes::Time,
+        Arel::Attributes::Boolean,
+        Arel::Attributes::Attribute
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary
+          assert_equal [:a, :b, binary], @collector.calls
+        end
+      end
+
+      def test_table
+        relation = Arel::Table.new(:users)
+        @visitor.accept relation
+        assert_equal ['users', relation], @collector.calls
+      end
+
+      def test_array
+        node = Nodes::Or.new(:a, :b)
+        list = [node]
+        @visitor.accept list
+        assert_equal [:a, :b, node, list], @collector.calls
+      end
+
+      def test_set
+        node = Nodes::Or.new(:a, :b)
+        set  = Set.new([node])
+        @visitor.accept set
+        assert_equal [:a, :b, node, set], @collector.calls
+      end
+
+      def test_hash
+        node = Nodes::Or.new(:a, :b)
+        hash = { node => node }
+        @visitor.accept hash
+        assert_equal [:a, :b, node, :a, :b, node, hash], @collector.calls
+      end
+
+      def test_update_statement
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = :a
+        stmt.values << :b
+        stmt.wheres << :c
+        stmt.orders << :d
+        stmt.limit = :e
+
+        @visitor.accept stmt
+        assert_equal [:a, :b, stmt.values, :c, stmt.wheres, :d, stmt.orders,
+          :e, stmt], @collector.calls
+      end
+
+      def test_select_core
+        core = Nodes::SelectCore.new
+        core.projections << :a
+        core.froms = :b
+        core.wheres << :c
+        core.groups << :d
+        core.windows << :e
+        core.havings << :f
+
+        @visitor.accept core
+        assert_equal [
+          :a, core.projections,
+          :b, [],
+          core.source,
+          :c, core.wheres,
+          :d, core.groups,
+          :e, core.windows,
+          :f, core.havings,
+          core], @collector.calls
+      end
+
+      def test_select_statement
+        ss = Nodes::SelectStatement.new
+        ss.cores.replace [:a]
+        ss.orders << :b
+        ss.limit = :c
+        ss.lock = :d
+        ss.offset = :e
+
+        @visitor.accept ss
+        assert_equal [
+          :a, ss.cores,
+          :b, ss.orders,
+          :c,
+          :d,
+          :e,
+          ss], @collector.calls
+      end
+
+      def test_insert_statement
+        stmt = Nodes::InsertStatement.new
+        stmt.relation = :a
+        stmt.columns << :b
+        stmt.values = :c
+
+        @visitor.accept stmt
+        assert_equal [:a, :b, stmt.columns, :c, stmt], @collector.calls
+      end
+
+      def test_case
+        node = Arel::Nodes::Case.new
+        node.case = :a
+        node.conditions << :b
+        node.default = :c
+
+        @visitor.accept node
+        assert_equal [:a, :b, node.conditions, :c, node], @collector.calls
+      end
+
+      def test_node
+        node = Nodes::Node.new
+        @visitor.accept node
+        assert_equal [node], @collector.calls
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb
new file mode 100644
index 0000000000..eb278cde4c
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+require_relative '../helper'
+require 'concurrent'
+
+module Arel
+  module Visitors
+    class DummyVisitor < Visitor
+      def initialize
+        super
+        @barrier = Concurrent::CyclicBarrier.new(2)
+      end
+
+      def visit_Arel_Visitors_DummySuperNode node
+        42
+      end
+
+      # This is terrible, but it's the only way to reliably reproduce
+      # the possible race where two threads attempt to correct the
+      # dispatch hash at the same time.
+      def send *args
+        super
+      rescue
+        # Both threads try (and fail) to dispatch to the subclass's name
+        @barrier.wait
+        raise
+      ensure
+        # Then one thread successfully completes (updating the dispatch
+        # table in the process) before the other finishes raising its
+        # exception.
+        Thread.current[:delay].wait if Thread.current[:delay]
+      end
+    end
+
+    class DummySuperNode
+    end
+
+    class DummySubNode < DummySuperNode
+    end
+
+    class DispatchContaminationTest < Arel::Spec
+      before do
+        @connection = Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      it 'dispatches properly after failing upwards' do
+        node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+
+        node.first # from Nodes::Node's Enumerable mixin
+
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+      end
+
+      it 'is threadsafe when implementing superclass fallback' do
+        visitor = DummyVisitor.new
+        main_thread_finished = Concurrent::Event.new
+
+        racing_thread = Thread.new do
+          Thread.current[:delay] = main_thread_finished
+          visitor.accept DummySubNode.new
+        end
+
+        assert_equal 42, visitor.accept(DummySubNode.new)
+        main_thread_finished.set
+
+        assert_equal 42, racing_thread.value
+      end
+    end
+  end
+end
+
diff --git a/activerecord/test/cases/arel/visitors/dot_test.rb b/activerecord/test/cases/arel/visitors/dot_test.rb
new file mode 100644
index 0000000000..048482c3ca
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/dot_test.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class TestDot < Arel::Test
+      def setup
+        @visitor = Visitors::Dot.new
+      end
+
+      # functions
+      [
+        Nodes::Sum,
+        Nodes::Exists,
+        Nodes::Max,
+        Nodes::Min,
+        Nodes::Avg,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a, "z")
+          @visitor.accept op, Collectors::PlainString.new
+        end
+      end
+
+      def test_named_function
+        func = Nodes::NamedFunction.new 'omg', 'omg'
+        @visitor.accept func, Collectors::PlainString.new
+      end
+
+      # unary ops
+      [
+        Arel::Nodes::Not,
+        Arel::Nodes::Group,
+        Arel::Nodes::On,
+        Arel::Nodes::Grouping,
+        Arel::Nodes::Offset,
+        Arel::Nodes::Ordering,
+        Arel::Nodes::UnqualifiedColumn,
+        Arel::Nodes::Top,
+        Arel::Nodes::Limit,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a)
+          @visitor.accept op, Collectors::PlainString.new
+        end
+      end
+
+      # binary ops
+      [
+        Arel::Nodes::Assignment,
+        Arel::Nodes::Between,
+        Arel::Nodes::DoesNotMatch,
+        Arel::Nodes::Equality,
+        Arel::Nodes::GreaterThan,
+        Arel::Nodes::GreaterThanOrEqual,
+        Arel::Nodes::In,
+        Arel::Nodes::LessThan,
+        Arel::Nodes::LessThanOrEqual,
+        Arel::Nodes::Matches,
+        Arel::Nodes::NotEqual,
+        Arel::Nodes::NotIn,
+        Arel::Nodes::Or,
+        Arel::Nodes::TableAlias,
+        Arel::Nodes::Values,
+        Arel::Nodes::As,
+        Arel::Nodes::DeleteStatement,
+        Arel::Nodes::JoinSource,
+        Arel::Nodes::Casted,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary, Collectors::PlainString.new
+        end
+      end
+
+      def test_Arel_Nodes_BindParam
+        node = Arel::Nodes::BindParam.new(1)
+        collector = Collectors::PlainString.new
+        assert_match '[label="<f0>Arel::Nodes::BindParam"]', @visitor.accept(node, collector).value
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/ibm_db_test.rb b/activerecord/test/cases/arel/visitors/ibm_db_test.rb
new file mode 100644
index 0000000000..d7569eedc3
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/ibm_db_test.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class IbmDbTest < Arel::Spec
+      before do
+        @visitor = IBM_DB.new Table.engine.connection
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'uses FETCH FIRST n ROWS to limit results' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FETCH FIRST 1 ROWS ONLY"
+      end
+
+      it 'uses FETCH FIRST n ROWS in updates with a limit' do
+        table = Table.new(:users)
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = table
+        stmt.limit = Nodes::Limit.new(Nodes.build_quoted(1))
+        stmt.key = table[:id]
+        sql = compile(stmt)
+        sql.must_be_like "UPDATE \"users\" WHERE \"users\".\"id\" IN (SELECT \"users\".\"id\" FROM \"users\" FETCH FIRST 1 ROWS ONLY)"
+      end
+
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/informix_test.rb b/activerecord/test/cases/arel/visitors/informix_test.rb
new file mode 100644
index 0000000000..bb6ff42f05
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/informix_test.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class InformixTest < Arel::Spec
+      before do
+        @visitor = Informix.new Table.engine.connection
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'uses FIRST n to limit results' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FIRST 1"
+      end
+
+      it 'uses FIRST n in updates with a limit' do
+        table = Table.new(:users)
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = table
+        stmt.limit = Nodes::Limit.new(Nodes.build_quoted(1))
+        stmt.key = table[:id]
+        sql = compile(stmt)
+        sql.must_be_like "UPDATE \"users\" WHERE \"users\".\"id\" IN (SELECT FIRST 1 \"users\".\"id\" FROM \"users\")"
+      end
+
+      it 'uses SKIP n to jump results' do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT SKIP 10"
+      end
+
+      it 'uses SKIP before FIRST' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        stmt.offset = Nodes::Offset.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT SKIP 1 FIRST 1"
+      end
+
+      it 'uses INNER JOIN to perform joins' do
+        core = Nodes::SelectCore.new
+        table = Table.new(:posts)
+        core.source = Nodes::JoinSource.new(table, [table.create_join(Table.new(:comments))])
+
+        stmt = Nodes::SelectStatement.new([core])
+        sql = compile(stmt)
+        sql.must_be_like 'SELECT FROM "posts" INNER JOIN "comments"'
+      end
+
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/mssql_test.rb b/activerecord/test/cases/arel/visitors/mssql_test.rb
new file mode 100644
index 0000000000..4e81678813
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/mssql_test.rb
@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class MssqlTest < Arel::Spec
+      before do
+        @visitor = MSSQL.new Table.engine.connection
+        @table = Arel::Table.new "users"
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'should not modify query if no offset or limit' do
+        stmt = Nodes::SelectStatement.new
+        sql = compile(stmt)
+        sql.must_be_like "SELECT"
+      end
+
+      it 'should go over table PK if no .order() or .group()' do
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.from = @table
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY \"users\".\"id\") as _row_num FROM \"users\") as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it 'caches the PK lookup for order' do
+        connection = Minitest::Mock.new
+        connection.expect(:primary_key, ["id"], ["users"])
+
+        # We don't care how many times these methods are called
+        def connection.quote_table_name(*); ""; end
+        def connection.quote_column_name(*); ""; end
+
+        @visitor = MSSQL.new(connection)
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.from = @table
+        stmt.limit = Nodes::Limit.new(10)
+
+        compile(stmt)
+        compile(stmt)
+
+        connection.verify
+      end
+
+      it 'should use TOP for limited deletes' do
+        stmt = Nodes::DeleteStatement.new
+        stmt.relation = @table
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+
+        sql.must_be_like "DELETE TOP (10) FROM \"users\""
+      end
+
+      it 'should go over query ORDER BY if .order()' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.orders << Nodes::SqlLiteral.new('order_by')
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY order_by) as _row_num) as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it 'should go over query GROUP BY if no .order() and there is .group()' do
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.groups << Nodes::SqlLiteral.new('group_by')
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY group_by) as _row_num GROUP BY group_by) as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it 'should use BETWEEN if both .limit() and .offset' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.offset = Nodes::Offset.new(20)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num BETWEEN 21 AND 30"
+      end
+
+      it 'should use >= if only .offset' do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(20)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num >= 21"
+      end
+
+      it 'should generate subquery for .count' do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.cores.first.projections << Nodes::Count.new('*')
+        sql = compile(stmt)
+        sql.must_be_like "SELECT COUNT(1) as count_id FROM (SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num BETWEEN 1 AND 10) AS subquery"
+      end
+
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/mysql_test.rb b/activerecord/test/cases/arel/visitors/mysql_test.rb
new file mode 100644
index 0000000000..f9b468b1d2
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/mysql_test.rb
@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class MysqlTest < Arel::Spec
+      before do
+        @visitor = MySQL.new Table.engine.connection
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'squashes parenthesis on multiple unions' do
+        subnode = Nodes::Union.new Arel.sql('left'), Arel.sql('right')
+        node    = Nodes::Union.new subnode, Arel.sql('topright')
+        assert_equal 1, compile(node).scan('(').length
+
+        subnode = Nodes::Union.new Arel.sql('left'), Arel.sql('right')
+        node    = Nodes::Union.new Arel.sql('topleft'), subnode
+        assert_equal 1, compile(node).scan('(').length
+      end
+
+      ###
+      # :'(
+      # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
+      it 'defaults limit to 18446744073709551615' do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FROM DUAL LIMIT 18446744073709551615 OFFSET 1"
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::UpdateStatement.new
+        sc.relation = Table.new(:users)
+        sc.limit = Nodes::Limit.new(Nodes.build_quoted("omg"))
+        assert_equal("UPDATE \"users\" LIMIT 'omg'", compile(sc))
+      end
+
+      it 'uses DUAL for empty from' do
+        stmt = Nodes::SelectStatement.new
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FROM DUAL"
+      end
+
+      describe 'locking' do
+        it 'defaults to FOR UPDATE when locking' do
+          node = Nodes::Lock.new(Arel.sql('FOR UPDATE'))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+
+        it 'allows a custom string to be used as a lock' do
+          node = Nodes::Lock.new(Arel.sql('LOCK IN SHARE MODE'))
+          compile(node).must_be_like "LOCK IN SHARE MODE"
+        end
+      end
+
+      describe "concat" do
+        it "concats columns" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(@table[:name])
+          compile(query).must_be_like %{
+            CONCAT("users"."name", "users"."name")
+          }
+        end
+
+        it "concats a string" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(Nodes.build_quoted('abc'))
+          compile(query).must_be_like %{
+            CONCAT("users"."name", 'abc')
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/oracle12_test.rb b/activerecord/test/cases/arel/visitors/oracle12_test.rb
new file mode 100644
index 0000000000..ef2050b7c9
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/oracle12_test.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class Oracle12Test < Arel::Spec
+      before do
+        @visitor = Oracle12.new Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'modified except to be minus' do
+        left = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 10")
+        right = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 20")
+        sql = compile Nodes::Except.new(left, right)
+        sql.must_be_like %{
+          ( SELECT * FROM users WHERE age > 10 MINUS SELECT * FROM users WHERE age > 20 )
+        }
+      end
+
+      it 'generates select options offset then limit' do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT OFFSET 1 ROWS FETCH FIRST 10 ROWS ONLY"
+      end
+
+      describe 'locking' do
+        it 'generates ArgumentError if limit and lock are used' do
+          stmt = Nodes::SelectStatement.new
+          stmt.limit = Nodes::Limit.new(10)
+          stmt.lock = Nodes::Lock.new(Arel.sql('FOR UPDATE'))
+          assert_raises ArgumentError do
+            compile(stmt)
+          end
+        end
+
+        it 'defaults to FOR UPDATE when locking' do
+          node = Nodes::Lock.new(Arel.sql('FOR UPDATE'))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = :a1 AND "users"."id" = :a2
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/oracle_test.rb b/activerecord/test/cases/arel/visitors/oracle_test.rb
new file mode 100644
index 0000000000..0737774fbf
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/oracle_test.rb
@@ -0,0 +1,196 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class OracleTest < Arel::Spec
+      before do
+        @visitor = Oracle.new Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'modifies order when there is distinct and first value' do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new('foo')
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__
+        }
+      end
+
+      it 'is idempotent with crazy query' do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new('foo')
+
+        sql = compile(stmt)
+        sql2 = compile(stmt)
+        sql.must_equal sql2
+      end
+
+      it 'splits orders with commas' do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new('foo, bar')
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__, alias_1__
+        }
+      end
+
+      it 'splits orders with commas and function calls' do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new('NVL(LOWER(bar, foo), foo) DESC, UPPER(baz)')
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__ DESC, alias_1__
+        }
+      end
+
+      describe 'Nodes::SelectStatement' do
+        describe 'limit' do
+          it 'adds a rownum clause' do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{ SELECT WHERE ROWNUM <= 10 }
+          end
+
+          it 'is idempotent' do
+            stmt = Nodes::SelectStatement.new
+            stmt.orders << Nodes::SqlLiteral.new('foo')
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql2 = compile stmt
+            sql.must_equal sql2
+          end
+
+          it 'creates a subquery when there is order_by' do
+            stmt = Nodes::SelectStatement.new
+            stmt.orders << Nodes::SqlLiteral.new('foo')
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT ORDER BY foo ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it 'creates a subquery when there is group by' do
+            stmt = Nodes::SelectStatement.new
+            stmt.cores.first.groups << Nodes::SqlLiteral.new('foo')
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT GROUP BY foo ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it 'creates a subquery when there is DISTINCT' do
+            stmt = Nodes::SelectStatement.new
+            stmt.cores.first.set_quantifier = Arel::Nodes::Distinct.new
+            stmt.cores.first.projections << Nodes::SqlLiteral.new('id')
+            stmt.limit = Arel::Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT DISTINCT id ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it 'creates a different subquery when there is an offset' do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT ) raw_sql_
+                 WHERE rownum <= 20
+              )
+              WHERE raw_rnum_ > 10
+            }
+          end
+
+          it 'creates a subquery when there is limit and offset with BindParams' do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(Nodes::BindParam.new(1))
+            stmt.offset = Nodes::Offset.new(Nodes::BindParam.new(1))
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT ) raw_sql_
+                 WHERE rownum <= (:a1 + :a2)
+              )
+              WHERE raw_rnum_ > :a3
+            }
+          end
+
+          it 'is idempotent with different subquery' do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql2 = compile stmt
+            sql.must_equal sql2
+          end
+        end
+
+        describe 'only offset' do
+          it 'creates a select from subquery with rownum condition' do
+            stmt = Nodes::SelectStatement.new
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT) raw_sql_
+              )
+              WHERE raw_rnum_ > 10
+            }
+          end
+        end
+      end
+
+      it 'modified except to be minus' do
+        left = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 10")
+        right = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 20")
+        sql = compile Nodes::Except.new(left, right)
+        sql.must_be_like %{
+          ( SELECT * FROM users WHERE age > 10 MINUS SELECT * FROM users WHERE age > 20 )
+        }
+      end
+
+      describe 'locking' do
+        it 'defaults to FOR UPDATE when locking' do
+          node = Nodes::Lock.new(Arel.sql('FOR UPDATE'))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = :a1 AND "users"."id" = :a2
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/postgres_test.rb b/activerecord/test/cases/arel/visitors/postgres_test.rb
new file mode 100644
index 0000000000..6aa786b14f
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/postgres_test.rb
@@ -0,0 +1,280 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class PostgresTest < Arel::Spec
+      before do
+        @visitor = PostgreSQL.new Table.engine.connection
+        @table = Table.new(:users)
+        @attr = @table[:id]
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      describe 'locking' do
+        it 'defaults to FOR UPDATE' do
+          compile(Nodes::Lock.new(Arel.sql('FOR UPDATE'))).must_be_like %{
+            FOR UPDATE
+          }
+        end
+
+        it 'allows a custom string to be used as a lock' do
+          node = Nodes::Lock.new(Arel.sql('FOR SHARE'))
+          compile(node).must_be_like %{
+            FOR SHARE
+          }
+        end
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::SelectStatement.new
+        sc.limit = Nodes::Limit.new(Nodes.build_quoted("omg"))
+        sc.cores.first.projections << Arel.sql('DISTINCT ON')
+        sc.orders << Arel.sql("xyz")
+        sql =  compile(sc)
+        assert_match(/LIMIT 'omg'/, sql)
+        assert_equal 1, sql.scan(/LIMIT/).length, 'should have one limit'
+      end
+
+      it 'should support DISTINCT ON' do
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::DistinctOn.new(Arel.sql('aaron'))
+        assert_match 'DISTINCT ON ( aaron )', compile(core)
+      end
+
+      it 'should support DISTINCT' do
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::Distinct.new
+        assert_equal 'SELECT DISTINCT', compile(core)
+      end
+
+      it 'encloses LATERAL queries in parens' do
+        subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+        compile(subquery.lateral).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%')
+        }
+      end
+
+      it 'produces LATERAL queries with alias' do
+        subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+        compile(subquery.lateral('bar')).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%') bar
+        }
+      end
+
+      describe "Nodes::Matches" do
+        it "should know how to visit" do
+          node = @table[:name].matches('foo%')
+          node.must_be_kind_of Nodes::Matches
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" ILIKE 'foo%'
+          }
+        end
+
+        it "should know how to visit case sensitive" do
+          node = @table[:name].matches('foo%', nil, true)
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].matches('foo!%', '!')
+          compile(node).must_be_like %{
+            "users"."name" ILIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::DoesNotMatch" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match('foo%')
+          node.must_be_kind_of Nodes::DoesNotMatch
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" NOT ILIKE 'foo%'
+          }
+        end
+
+        it "should know how to visit case sensitive" do
+          node = @table[:name].does_not_match('foo%', nil, true)
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].does_not_match('foo!%', '!')
+          compile(node).must_be_like %{
+            "users"."name" NOT ILIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].does_not_match('foo%'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" NOT ILIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::Regexp" do
+        it "should know how to visit" do
+          node = @table[:name].matches_regexp('foo.*')
+          node.must_be_kind_of Nodes::Regexp
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" ~ 'foo.*'
+          }
+        end
+
+        it "can handle case insensitive" do
+          node = @table[:name].matches_regexp('foo.*', false)
+          node.must_be_kind_of Nodes::Regexp
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" ~* 'foo.*'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].matches_regexp('foo.*'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" ~ 'foo.*')
+          }
+        end
+      end
+
+      describe "Nodes::NotRegexp" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match_regexp('foo.*')
+          node.must_be_kind_of Nodes::NotRegexp
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" !~ 'foo.*'
+          }
+        end
+
+        it "can handle case insensitive" do
+          node = @table[:name].does_not_match_regexp('foo.*', false)
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" !~* 'foo.*'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].does_not_match_regexp('foo.*'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" !~ 'foo.*')
+          }
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = $1 AND "users"."id" = $2
+          }
+        end
+      end
+
+      describe "Nodes::Cube" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::Cube.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            CUBE( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          dimensions = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::Cube.new(dimensions)
+          compile(node).must_be_like %{
+            CUBE( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate paranthesis when supplied with many Dimensions" do
+          dim1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          dim2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::Cube.new([dim1, dim2])
+          compile(node).must_be_like %{
+            CUBE( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+
+      describe "Nodes::GroupingSet" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::GroupingSet.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            GROUPING SET( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          group = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::GroupingSet.new(group)
+          compile(node).must_be_like %{
+            GROUPING SET( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate paranthesis when supplied with many Dimensions" do
+          group1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          group2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::GroupingSet.new([group1, group2])
+          compile(node).must_be_like %{
+            GROUPING SET( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+
+      describe "Nodes::RollUp" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::RollUp.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            ROLLUP( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          group = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::RollUp.new(group)
+          compile(node).must_be_like %{
+            ROLLUP( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate paranthesis when supplied with many Dimensions" do
+          group1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          group2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::RollUp.new([group1, group2])
+          compile(node).must_be_like %{
+            ROLLUP( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/sqlite_test.rb b/activerecord/test/cases/arel/visitors/sqlite_test.rb
new file mode 100644
index 0000000000..23f66ee096
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/sqlite_test.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+require_relative '../helper'
+
+module Arel
+  module Visitors
+    class SqliteTest < Arel::Spec
+      before do
+        @visitor = SQLite.new Table.engine.connection_pool
+      end
+
+      it 'defaults limit to -1' do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        sql = @visitor.accept(stmt, Collectors::SQLString.new).value
+        sql.must_be_like "SELECT LIMIT -1 OFFSET 1"
+      end
+
+      it 'does not support locking' do
+        node = Nodes::Lock.new(Arel.sql('FOR UPDATE'))
+        assert_equal '', @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'does not support boolean' do
+        node = Nodes::True.new()
+        assert_equal '1', @visitor.accept(node, Collectors::SQLString.new).value
+        node = Nodes::False.new()
+        assert_equal '0', @visitor.accept(node, Collectors::SQLString.new).value
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/to_sql_test.rb b/activerecord/test/cases/arel/visitors/to_sql_test.rb
new file mode 100644
index 0000000000..1503bcd578
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/to_sql_test.rb
@@ -0,0 +1,653 @@
+# frozen_string_literal: true
+require_relative '../helper'
+require 'bigdecimal'
+
+module Arel
+  module Visitors
+    describe 'the to_sql visitor' do
+      before do
+        @conn = FakeRecord::Base.new
+        @visitor = ToSql.new @conn.connection
+        @table = Table.new(:users)
+        @attr = @table[:id]
+      end
+
+      def compile node
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it 'works with BindParams' do
+        node = Nodes::BindParam.new(1)
+        sql = compile node
+        sql.must_be_like '?'
+      end
+
+      it 'does not quote BindParams used as part of a Values' do
+        bp = Nodes::BindParam.new(1)
+        values = Nodes::Values.new([bp])
+        sql = compile values
+        sql.must_be_like 'VALUES (?)'
+      end
+
+      it 'can define a dispatch method' do
+        visited = false
+        viz = Class.new(Arel::Visitors::Visitor) {
+          define_method(:hello) do |node, c|
+            visited = true
+          end
+
+          def dispatch
+            { Arel::Table => 'hello' }
+          end
+        }.new
+
+        viz.accept(@table, Collectors::SQLString.new)
+        assert visited, 'hello method was called'
+      end
+
+      it 'should not quote sql literals' do
+        node = @table[Arel.star]
+        sql = compile node
+        sql.must_be_like '"users".*'
+      end
+
+      it 'should visit named functions' do
+        function = Nodes::NamedFunction.new('omg', [Arel.star])
+        assert_equal 'omg(*)', compile(function)
+      end
+
+      it 'should chain predications on named functions' do
+        function = Nodes::NamedFunction.new('omg', [Arel.star])
+        sql = compile(function.eq(2))
+        sql.must_be_like %{ omg(*) = 2 }
+      end
+
+      it 'should handle nil with named functions' do
+        function = Nodes::NamedFunction.new('omg', [Arel.star])
+        sql = compile(function.eq(nil))
+        sql.must_be_like %{ omg(*) IS NULL }
+      end
+
+      it 'should visit built-in functions' do
+        function = Nodes::Count.new([Arel.star])
+        assert_equal 'COUNT(*)', compile(function)
+
+        function = Nodes::Sum.new([Arel.star])
+        assert_equal 'SUM(*)', compile(function)
+
+        function = Nodes::Max.new([Arel.star])
+        assert_equal 'MAX(*)', compile(function)
+
+        function = Nodes::Min.new([Arel.star])
+        assert_equal 'MIN(*)', compile(function)
+
+        function = Nodes::Avg.new([Arel.star])
+        assert_equal 'AVG(*)', compile(function)
+      end
+
+      it 'should visit built-in functions operating on distinct values' do
+        function = Nodes::Count.new([Arel.star])
+        function.distinct = true
+        assert_equal 'COUNT(DISTINCT *)', compile(function)
+
+        function = Nodes::Sum.new([Arel.star])
+        function.distinct = true
+        assert_equal 'SUM(DISTINCT *)', compile(function)
+
+        function = Nodes::Max.new([Arel.star])
+        function.distinct = true
+        assert_equal 'MAX(DISTINCT *)', compile(function)
+
+        function = Nodes::Min.new([Arel.star])
+        function.distinct = true
+        assert_equal 'MIN(DISTINCT *)', compile(function)
+
+        function = Nodes::Avg.new([Arel.star])
+        function.distinct = true
+        assert_equal 'AVG(DISTINCT *)', compile(function)
+      end
+
+      it 'works with lists' do
+        function = Nodes::NamedFunction.new('omg', [Arel.star, Arel.star])
+        assert_equal 'omg(*, *)', compile(function)
+      end
+
+      describe 'Nodes::Equality' do
+        it "should escape strings" do
+          test = Table.new(:users)[:name].eq 'Aaron Patterson'
+          compile(test).must_be_like %{
+            "users"."name" = 'Aaron Patterson'
+          }
+        end
+
+        it 'should handle false' do
+          table = Table.new(:users)
+          val = Nodes.build_quoted(false, table[:active])
+          sql = compile Nodes::Equality.new(val, val)
+          sql.must_be_like %{ 'f' = 'f' }
+        end
+
+        it 'should handle nil' do
+          sql = compile Nodes::Equality.new(@table[:name], nil)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe 'Nodes::Grouping' do
+        it 'wraps nested groupings in brackets only once' do
+          sql = compile Nodes::Grouping.new(Nodes::Grouping.new(Nodes.build_quoted('foo')))
+          sql.must_equal "('foo')"
+        end
+      end
+
+      describe 'Nodes::NotEqual' do
+        it 'should handle false' do
+          val = Nodes.build_quoted(false, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:active], val)
+          sql.must_be_like %{ "users"."active" != 'f' }
+        end
+
+        it 'should handle nil' do
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+
+      it "should visit string subclass" do
+        [
+          Class.new(String).new(":'("),
+          Class.new(Class.new(String)).new(":'("),
+        ].each do |obj|
+          val = Nodes.build_quoted(obj, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" != ':\\'(' }
+        end
+      end
+
+      it "should visit_Class" do
+        compile(Nodes.build_quoted(DateTime)).must_equal "'DateTime'"
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::SelectStatement.new
+        sc.limit = Arel::Nodes::Limit.new(Nodes.build_quoted("omg"))
+        assert_match(/LIMIT 'omg'/, compile(sc))
+      end
+
+      it "should contain a single space before ORDER BY" do
+        table = Table.new(:users)
+        test = table.order(table[:name])
+        sql = compile test
+        assert_match(/"users" ORDER BY/, sql)
+      end
+
+      it "should quote LIMIT without column type coercion" do
+        table = Table.new(:users)
+        sc = table.where(table[:name].eq(0)).take(1).ast
+        assert_match(/WHERE "users"."name" = 0 LIMIT 1/, compile(sc))
+      end
+
+      it "should visit_DateTime" do
+        dt = DateTime.now
+        table = Table.new(:users)
+        test = table[:created_at].eq dt
+        sql = compile test
+
+        sql.must_be_like %{"users"."created_at" = '#{dt.strftime("%Y-%m-%d %H:%M:%S")}'}
+      end
+
+      it "should visit_Float" do
+        test = Table.new(:products)[:price].eq 2.14
+        sql = compile test
+        sql.must_be_like %{"products"."price" = 2.14}
+      end
+
+      it "should visit_Not" do
+        sql = compile Nodes::Not.new(Arel.sql("foo"))
+        sql.must_be_like "NOT (foo)"
+      end
+
+      it "should apply Not to the whole expression" do
+        node = Nodes::And.new [@attr.eq(10), @attr.eq(11)]
+        sql = compile Nodes::Not.new(node)
+        sql.must_be_like %{NOT ("users"."id" = 10 AND "users"."id" = 11)}
+      end
+
+      it "should visit_As" do
+        as = Nodes::As.new(Arel.sql("foo"), Arel.sql("bar"))
+        sql = compile as
+        sql.must_be_like "foo AS bar"
+      end
+
+      it "should visit_Bignum" do
+        compile 8787878092
+      end
+
+      it "should visit_Hash" do
+        compile(Nodes.build_quoted({:a => 1}))
+      end
+
+      it "should visit_Set" do
+        compile Nodes.build_quoted(Set.new([1, 2]))
+      end
+
+      it "should visit_BigDecimal" do
+        compile Nodes.build_quoted(BigDecimal('2.14'))
+      end
+
+      it "should visit_Date" do
+        dt = Date.today
+        table = Table.new(:users)
+        test = table[:created_at].eq dt
+        sql = compile test
+
+        sql.must_be_like %{"users"."created_at" = '#{dt.strftime("%Y-%m-%d")}'}
+      end
+
+      it "should visit_NilClass" do
+        compile(Nodes.build_quoted(nil)).must_be_like "NULL"
+      end
+
+      it "unsupported input should raise UnsupportedVisitError" do
+        error = assert_raises(UnsupportedVisitError) { compile(nil) }
+        assert_match(/\AUnsupported/, error.message)
+      end
+
+      it "should visit_Arel_SelectManager, which is a subquery" do
+        mgr = Table.new(:foo).project(:bar)
+        compile(mgr).must_be_like '(SELECT bar FROM "foo")'
+      end
+
+      it "should visit_Arel_Nodes_And" do
+        node = Nodes::And.new [@attr.eq(10), @attr.eq(11)]
+        compile(node).must_be_like %{
+          "users"."id" = 10 AND "users"."id" = 11
+        }
+      end
+
+      it "should visit_Arel_Nodes_Or" do
+        node = Nodes::Or.new @attr.eq(10), @attr.eq(11)
+        compile(node).must_be_like %{
+          "users"."id" = 10 OR "users"."id" = 11
+        }
+      end
+
+      it "should visit_Arel_Nodes_Assignment" do
+        column = @table["id"]
+        node = Nodes::Assignment.new(
+          Nodes::UnqualifiedColumn.new(column),
+          Nodes::UnqualifiedColumn.new(column)
+        )
+        compile(node).must_be_like %{
+          "id" = "id"
+        }
+      end
+
+      it "should visit visit_Arel_Attributes_Time" do
+        attr = Attributes::Time.new(@attr.relation, @attr.name)
+        compile attr
+      end
+
+      it "should visit_TrueClass" do
+        test = Table.new(:users)[:bool].eq(true)
+        compile(test).must_be_like %{ "users"."bool" = 't' }
+      end
+
+      describe "Nodes::Matches" do
+        it "should know how to visit" do
+          node = @table[:name].matches('foo%')
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].matches('foo!%', '!')
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].matches('foo%'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" LIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::DoesNotMatch" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match('foo%')
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].does_not_match('foo!%', '!')
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it 'can handle subqueries' do
+          subquery = @table.project(:id).where(@table[:name].does_not_match('foo%'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" NOT LIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::Ordering" do
+        it "should know how to visit" do
+          node = @attr.desc
+          compile(node).must_be_like %{
+            "users"."id" DESC
+          }
+        end
+      end
+
+      describe "Nodes::In" do
+        it "should know how to visit" do
+          node = @attr.in [1, 2, 3]
+          compile(node).must_be_like %{
+            "users"."id" IN (1, 2, 3)
+          }
+        end
+
+        it "should return 1=0 when empty right which is always false" do
+          node = @attr.in []
+          compile(node).must_equal '1=0'
+        end
+
+        it 'can handle two dot ranges' do
+          node = @attr.between 1..3
+          compile(node).must_be_like %{
+            "users"."id" BETWEEN 1 AND 3
+          }
+        end
+
+        it 'can handle three dot ranges' do
+          node = @attr.between 1...3
+          compile(node).must_be_like %{
+            "users"."id" >= 1 AND "users"."id" < 3
+          }
+        end
+
+        it 'can handle ranges bounded by infinity' do
+          node = @attr.between 1..Float::INFINITY
+          compile(node).must_be_like %{
+            "users"."id" >= 1
+          }
+          node = @attr.between(-Float::INFINITY..3)
+          compile(node).must_be_like %{
+            "users"."id" <= 3
+          }
+          node = @attr.between(-Float::INFINITY...3)
+          compile(node).must_be_like %{
+            "users"."id" < 3
+          }
+          node = @attr.between(-Float::INFINITY..Float::INFINITY)
+          compile(node).must_be_like %{1=1}
+        end
+
+        it 'can handle subqueries' do
+          table = Table.new(:users)
+          subquery = table.project(:id).where(table[:name].eq('Aaron'))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" = 'Aaron')
+          }
+        end
+      end
+
+      describe "Nodes::InfixOperation" do
+        it "should handle Multiplication" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) * Arel::Attributes::Decimal.new(Table.new(:currency_rates), :rate)
+          compile(node).must_equal %("products"."price" * "currency_rates"."rate")
+        end
+
+        it "should handle Division" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) / 5
+          compile(node).must_equal %("products"."price" / 5)
+        end
+
+        it "should handle Addition" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) + 6
+          compile(node).must_equal %(("products"."price" + 6))
+        end
+
+        it "should handle Subtraction" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) - 7
+          compile(node).must_equal %(("products"."price" - 7))
+        end
+
+        it "should handle Concatination" do
+          table = Table.new(:users)
+          node = table[:name].concat(table[:name])
+          compile(node).must_equal %("users"."name" || "users"."name")
+        end
+
+        it "should handle BitwiseAnd" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) & 16
+          compile(node).must_equal %(("products"."bitmap" & 16))
+        end
+
+        it "should handle BitwiseOr" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) | 16
+          compile(node).must_equal %(("products"."bitmap" | 16))
+        end
+
+        it "should handle BitwiseXor" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) ^ 16
+          compile(node).must_equal %(("products"."bitmap" ^ 16))
+        end
+
+        it "should handle BitwiseShiftLeft" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) << 4
+          compile(node).must_equal %(("products"."bitmap" << 4))
+        end
+
+        it "should handle BitwiseShiftRight" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) >> 4
+          compile(node).must_equal %(("products"."bitmap" >> 4))
+        end
+
+        it "should handle arbitrary operators" do
+          node = Arel::Nodes::InfixOperation.new(
+            '&&',
+            Arel::Attributes::String.new(Table.new(:products), :name),
+            Arel::Attributes::String.new(Table.new(:products), :name)
+          )
+          compile(node).must_equal %("products"."name" && "products"."name")
+        end
+      end
+
+      describe "Nodes::UnaryOperation" do
+        it "should handle BitwiseNot" do
+          node = ~ Arel::Attributes::Integer.new(Table.new(:products), :bitmap)
+          compile(node).must_equal %( ~ "products"."bitmap")
+        end
+
+        it "should handle arbitrary operators" do
+          node = Arel::Nodes::UnaryOperation.new('!', Arel::Attributes::String.new(Table.new(:products), :active))
+          compile(node).must_equal %( ! "products"."active")
+        end
+      end
+
+      describe "Nodes::NotIn" do
+        it "should know how to visit" do
+          node = @attr.not_in [1, 2, 3]
+          compile(node).must_be_like %{
+            "users"."id" NOT IN (1, 2, 3)
+          }
+        end
+
+        it "should return 1=1 when empty right which is always true" do
+          node = @attr.not_in []
+          compile(node).must_equal '1=1'
+        end
+
+        it 'can handle two dot ranges' do
+          node = @attr.not_between 1..3
+          compile(node).must_equal(
+            %{("users"."id" < 1 OR "users"."id" > 3)}
+          )
+        end
+
+        it 'can handle three dot ranges' do
+          node = @attr.not_between 1...3
+          compile(node).must_equal(
+            %{("users"."id" < 1 OR "users"."id" >= 3)}
+          )
+        end
+
+        it 'can handle ranges bounded by infinity' do
+          node = @attr.not_between 1..Float::INFINITY
+          compile(node).must_be_like %{
+            "users"."id" < 1
+          }
+          node = @attr.not_between(-Float::INFINITY..3)
+          compile(node).must_be_like %{
+            "users"."id" > 3
+          }
+          node = @attr.not_between(-Float::INFINITY...3)
+          compile(node).must_be_like %{
+            "users"."id" >= 3
+          }
+          node = @attr.not_between(-Float::INFINITY..Float::INFINITY)
+          compile(node).must_be_like %{1=0}
+        end
+
+        it 'can handle subqueries' do
+          table = Table.new(:users)
+          subquery = table.project(:id).where(table[:name].eq('Aaron'))
+          node = @attr.not_in subquery
+          compile(node).must_be_like %{
+            "users"."id" NOT IN (SELECT id FROM "users" WHERE "users"."name" = 'Aaron')
+          }
+        end
+      end
+
+      describe 'Constants' do
+        it "should handle true" do
+          test = Table.new(:users).create_true
+          compile(test).must_be_like %{
+            TRUE
+          }
+        end
+
+        it "should handle false" do
+          test = Table.new(:users).create_false
+          compile(test).must_be_like %{
+            FALSE
+          }
+        end
+      end
+
+      describe 'TableAlias' do
+        it "should use the underlying table for checking columns" do
+          test = Table.new(:users).alias('zomgusers')[:id].eq '3'
+          compile(test).must_be_like %{
+            "zomgusers"."id" = '3'
+          }
+        end
+      end
+
+      describe 'distinct on' do
+        it 'raises not implemented error' do
+          core = Arel::Nodes::SelectCore.new
+          core.set_quantifier = Arel::Nodes::DistinctOn.new(Arel.sql('aaron'))
+
+          assert_raises(NotImplementedError) do
+            compile(core)
+          end
+        end
+      end
+
+      describe 'Nodes::Regexp' do
+        it 'raises not implemented error' do
+          node = Arel::Nodes::Regexp.new(@table[:name], Nodes.build_quoted('foo%'))
+
+          assert_raises(NotImplementedError) do
+            compile(node)
+          end
+        end
+      end
+
+      describe 'Nodes::NotRegexp' do
+        it 'raises not implemented error' do
+          node = Arel::Nodes::NotRegexp.new(@table[:name], Nodes.build_quoted('foo%'))
+
+          assert_raises(NotImplementedError) do
+            compile(node)
+          end
+        end
+      end
+
+      describe 'Nodes::Case' do
+        it 'supports simple case expressions' do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when('foo').then(1)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 ELSE 0 END
+          }
+        end
+
+        it 'supports extended case expressions' do
+          node = Arel::Nodes::Case.new
+            .when(@table[:name].in(%w(foo bar))).then(1)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE WHEN "users"."name" IN ('foo', 'bar') THEN 1 ELSE 0 END
+          }
+        end
+
+        it 'works without default branch' do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when('foo').then(1)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 END
+          }
+        end
+
+        it 'allows chaining multiple conditions' do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when('foo').then(1)
+            .when('bar').then(2)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 WHEN 'bar' THEN 2 ELSE 0 END
+          }
+        end
+
+        it 'supports #when with two arguments and no #then' do
+          node = Arel::Nodes::Case.new @table[:name]
+
+          { foo: 1, bar: 0 }.reduce(node) { |_node, pair| _node.when(*pair) }
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 WHEN 'bar' THEN 0 END
+          }
+        end
+
+        it 'can be chained as a predicate' do
+          node = @table[:name].when('foo').then('bar').else('baz')
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 'bar' ELSE 'baz' END
+          }
+        end
+      end
+    end
+  end
+end