10 files changed, 134 insertions, 32 deletions
diff --git a/activerecord/lib/arel/visitors/depth_first.rb b/activerecord/lib/arel/visitors/depth_first.rb
index 8f65d303ac..92d309453c 100644
--- a/activerecord/lib/arel/visitors/depth_first.rb
+++ b/activerecord/lib/arel/visitors/depth_first.rb
@@ -95,6 +95,8 @@ module Arel # :nodoc: all
         alias :visit_Arel_Nodes_NotEqual           :binary
         alias :visit_Arel_Nodes_NotIn              :binary
         alias :visit_Arel_Nodes_NotRegexp          :binary
+        alias :visit_Arel_Nodes_IsNotDistinctFrom  :binary
+        alias :visit_Arel_Nodes_IsDistinctFrom     :binary
         alias :visit_Arel_Nodes_Or                 :binary
         alias :visit_Arel_Nodes_OuterJoin          :binary
         alias :visit_Arel_Nodes_Regexp             :binary
diff --git a/activerecord/lib/arel/visitors/dot.rb b/activerecord/lib/arel/visitors/dot.rb
index 9054f0159b..6389c875cb 100644
--- a/activerecord/lib/arel/visitors/dot.rb
+++ b/activerecord/lib/arel/visitors/dot.rb
@@ -195,6 +195,8 @@ module Arel # :nodoc: all
         alias :visit_Arel_Nodes_JoinSource         :binary
         alias :visit_Arel_Nodes_LessThan           :binary
         alias :visit_Arel_Nodes_LessThanOrEqual    :binary
+        alias :visit_Arel_Nodes_IsNotDistinctFrom  :binary
+        alias :visit_Arel_Nodes_IsDistinctFrom     :binary
         alias :visit_Arel_Nodes_Matches            :binary
         alias :visit_Arel_Nodes_NotEqual           :binary
         alias :visit_Arel_Nodes_NotIn              :binary
diff --git a/activerecord/lib/arel/visitors/ibm_db.rb b/activerecord/lib/arel/visitors/ibm_db.rb
index 0a06aef60b..73166054da 100644
--- a/activerecord/lib/arel/visitors/ibm_db.rb
+++ b/activerecord/lib/arel/visitors/ibm_db.rb
@@ -10,6 +10,12 @@ module Arel # :nodoc: all
           collector = visit o.expr, collector
           collector << " ROWS ONLY"
         end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
     end
   end
 end
diff --git a/activerecord/lib/arel/visitors/mssql.rb b/activerecord/lib/arel/visitors/mssql.rb
index d564e19089..fdd864b40d 100644
--- a/activerecord/lib/arel/visitors/mssql.rb
+++ b/activerecord/lib/arel/visitors/mssql.rb
@@ -12,6 +12,31 @@ module Arel # :nodoc: all
 
       private
 
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          right = o.right
+
+          if right.nil?
+            collector = visit o.left, collector
+            collector << " IS NULL"
+          else
+            collector << "EXISTS (VALUES ("
+            collector = visit o.left, collector
+            collector << ") INTERSECT VALUES ("
+            collector = visit right, collector
+            collector << "))"
+          end
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NOT NULL"
+          else
+            collector << "NOT "
+            visit_Arel_Nodes_IsNotDistinctFrom o, collector
+          end
+        end
+
         def visit_Arel_Visitors_MSSQL_RowNumber(o, collector)
           collector << "ROW_NUMBER() OVER (ORDER BY "
           inject_join(o.children, collector, ", ") << ") as _row_num"
diff --git a/activerecord/lib/arel/visitors/mysql.rb b/activerecord/lib/arel/visitors/mysql.rb
index 32f6705d04..dd77cfdf66 100644
--- a/activerecord/lib/arel/visitors/mysql.rb
+++ b/activerecord/lib/arel/visitors/mysql.rb
@@ -4,34 +4,6 @@ module Arel # :nodoc: all
   module Visitors
     class MySQL < Arel::Visitors::ToSql
       private
-        def visit_Arel_Nodes_Union(o, collector, suppress_parens = false)
-          unless suppress_parens
-            collector << "( "
-          end
-
-          case o.left
-          when Arel::Nodes::Union
-            visit_Arel_Nodes_Union o.left, collector, true
-          else
-            visit o.left, collector
-          end
-
-          collector << " UNION "
-
-          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
@@ -65,6 +37,17 @@ module Arel # :nodoc: all
           collector
         end
 
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " <=> "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector << "NOT "
+          visit_Arel_Nodes_IsNotDistinctFrom o, collector
+        end
+
         # In the simple case, MySQL allows us to place JOINs directly into the UPDATE
         # query. However, this does not allow for LIMIT, OFFSET and ORDER. To support
         # these, we must use a subquery.
diff --git a/activerecord/lib/arel/visitors/oracle.rb b/activerecord/lib/arel/visitors/oracle.rb
index 30a1529d46..f96bf65ee5 100644
--- a/activerecord/lib/arel/visitors/oracle.rb
+++ b/activerecord/lib/arel/visitors/oracle.rb
@@ -148,6 +148,12 @@ module Arel # :nodoc: all
         def visit_Arel_Nodes_BindParam(o, collector)
           collector.add_bind(o.value) { |i| ":a#{i}" }
         end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
     end
   end
 end
diff --git a/activerecord/lib/arel/visitors/oracle12.rb b/activerecord/lib/arel/visitors/oracle12.rb
index 7061f06087..b092aa95e0 100644
--- a/activerecord/lib/arel/visitors/oracle12.rb
+++ b/activerecord/lib/arel/visitors/oracle12.rb
@@ -56,6 +56,12 @@ module Arel # :nodoc: all
         def visit_Arel_Nodes_BindParam(o, collector)
           collector.add_bind(o.value) { |i| ":a#{i}" }
         end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
     end
   end
 end
diff --git a/activerecord/lib/arel/visitors/postgresql.rb b/activerecord/lib/arel/visitors/postgresql.rb
index c5110fa89c..920776b4dc 100644
--- a/activerecord/lib/arel/visitors/postgresql.rb
+++ b/activerecord/lib/arel/visitors/postgresql.rb
@@ -77,6 +77,18 @@ module Arel # :nodoc: all
           grouping_parentheses o, collector
         end
 
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS NOT DISTINCT FROM "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS DISTINCT FROM "
+          visit o.right, collector
+        end
+
         # Used by Lateral visitor to enclose select queries in parentheses
         def grouping_parentheses(o, collector)
           if o.expr.is_a? Nodes::SelectStatement
diff --git a/activerecord/lib/arel/visitors/sqlite.rb b/activerecord/lib/arel/visitors/sqlite.rb
index cb1d2424ad..af6f7e856a 100644
--- a/activerecord/lib/arel/visitors/sqlite.rb
+++ b/activerecord/lib/arel/visitors/sqlite.rb
@@ -22,6 +22,18 @@ module Arel # :nodoc: all
         def visit_Arel_Nodes_False(o, collector)
           collector << "0"
         end
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS NOT "
+          visit o.right, collector
+        end
     end
   end
 end
diff --git a/activerecord/lib/arel/visitors/to_sql.rb b/activerecord/lib/arel/visitors/to_sql.rb
index 8e56fb55a2..f9fe4404eb 100644
--- a/activerecord/lib/arel/visitors/to_sql.rb
+++ b/activerecord/lib/arel/visitors/to_sql.rb
@@ -268,13 +268,11 @@ module Arel # :nodoc: all
         end
 
         def visit_Arel_Nodes_Union(o, collector)
-          collector << "( "
-          infix_value(o, collector, " UNION ") << " )"
+          infix_value_with_paren(o, collector, " UNION ")
         end
 
         def visit_Arel_Nodes_UnionAll(o, collector)
-          collector << "( "
-          infix_value(o, collector, " UNION ALL ") << " )"
+          infix_value_with_paren(o, collector, " UNION ALL ")
         end
 
         def visit_Arel_Nodes_Intersect(o, collector)
@@ -643,6 +641,26 @@ module Arel # :nodoc: all
           end
         end
 
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 0"
+          end
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NOT NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 1"
+          end
+        end
+
         def visit_Arel_Nodes_NotEqual(o, collector)
           right = o.right
 
@@ -845,6 +863,23 @@ module Arel # :nodoc: all
           visit o.right, collector
         end
 
+        def infix_value_with_paren(o, collector, value, suppress_parens = false)
+          collector << "( " unless suppress_parens
+          collector = if o.left.class == o.class
+            infix_value_with_paren(o.left, collector, value, true)
+          else
+            visit o.left, collector
+          end
+          collector << value
+          collector = if o.right.class == o.class
+            infix_value_with_paren(o.right, collector, value, true)
+          else
+            visit o.right, collector
+          end
+          collector << " )" unless suppress_parens
+          collector
+        end
+
         def aggregate(name, o, collector)
           collector << "#{name}("
           if o.distinct
@@ -858,6 +893,19 @@ module Arel # :nodoc: all
             collector
           end
         end
+
+        def is_distinct_from(o, collector)
+          collector << "CASE WHEN "
+          collector = visit o.left, collector
+          collector << " = "
+          collector = visit o.right, collector
+          collector << " OR ("
+          collector = visit o.left, collector
+          collector << " IS NULL AND "
+          collector = visit o.right, collector
+          collector << " IS NULL)"
+          collector << " THEN 0 ELSE 1 END"
+        end
     end
   end
 end