1 files changed, 30 insertions, 27 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 5ebd8a8dcb..f5b5482efb 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -31,8 +31,6 @@ module ActiveRecord
         def extract_default
           if blob_or_text_column?
             @default = null || strict ? nil : ''
-          elsif missing_default_forged_as_empty_string?(default)
-            @default = nil
           end
         end
 
@@ -59,17 +57,6 @@ module ActiveRecord
 
         private
 
-        # MySQL misreports NOT NULL column default when none is given.
-        # We can't detect this for columns which may have a legitimate ''
-        # default (string) but we can for others (integer, datetime, boolean,
-        # and the rest).
-        #
-        # Test whether the column has default '', is not null, and is not
-        # a type allowing default ''.
-        def missing_default_forged_as_empty_string?(default)
-          type != :string && !null && default == ''
-        end
-
         def assert_valid_default(default)
           if blob_or_text_column? && default.present?
             raise ArgumentError, "#{type} columns cannot have a default value: #{default.inspect}"
@@ -636,6 +623,7 @@ module ActiveRecord
       # it can be helpful to provide these in a migration's +change+ method so it can be reverted.
       # In that case, +options+ and the block will be used by create_table.
       def drop_table(table_name, options = {})
+        create_table_info_cache.delete(table_name) if create_table_info_cache.key?(table_name)
         execute "DROP#{' TEMPORARY' if options[:temporary]} TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
       end
 
@@ -764,16 +752,11 @@ module ActiveRecord
         SQL
       end
 
-      def case_sensitive_modifier(node, table_attribute)
-        node = Arel::Nodes.build_quoted node, table_attribute
-        Arel::Nodes::Bin.new(node)
-      end
-
       def case_sensitive_comparison(table, attribute, column, value)
-        if column.case_sensitive?
-          table[attribute].eq(value)
-        else
+        if value.nil? || column.case_sensitive?
           super
+        else
+          table[attribute].eq(Arel::Nodes::Bin.new(Arel::Nodes::BindParam.new))
         end
       end
 
@@ -781,10 +764,25 @@ module ActiveRecord
         if column.case_sensitive?
           super
         else
-          table[attribute].eq(value)
+          table[attribute].eq(Arel::Nodes::BindParam.new)
         end
       end
 
+      # In MySQL 5.7.5 and up, ONLY_FULL_GROUP_BY affects handling of queries that use
+      # DISTINCT and ORDER BY. It requires the ORDER BY columns in the select list for
+      # distinct queries, and requires that the ORDER BY include the distinct column.
+      # See https://dev.mysql.com/doc/refman/5.7/en/group-by-handling.html
+      def columns_for_distinct(columns, orders) # :nodoc:
+        order_columns = orders.reject(&:blank?).map { |s|
+          # Convert Arel node to string
+          s = s.to_sql unless s.is_a?(String)
+          # Remove any ASC/DESC modifiers
+          s.gsub(/\s+(?:ASC|DESC)\b/i, '')
+        }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
+
+        [super, *order_columns].join(', ')
+      end
+
       def strict_mode?
         self.class.type_cast_config_to_boolean(@config.fetch(:strict, true))
       end
@@ -964,11 +962,13 @@ module ActiveRecord
         subsubselect = select.clone
         subsubselect.projections = [key]
 
+        # Materialize subquery by adding distinct
+        # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
+        subsubselect.distinct unless select.limit || select.offset || select.orders.any?
+
         subselect = Arel::SelectManager.new(select.engine)
         subselect.project Arel.sql(key.name)
-        # Materialized subquery by adding distinct
-        # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
-        subselect.from subsubselect.distinct.as('__active_record_temp')
+        subselect.from subsubselect.as('__active_record_temp')
       end
 
       def mariadb?
@@ -1031,9 +1031,12 @@ module ActiveRecord
         end
       end
 
+      def create_table_info_cache # :nodoc:
+        @create_table_info_cache ||= {}
+      end
+
       def create_table_info(table_name) # :nodoc:
-        @create_table_info_cache = {}
-        @create_table_info_cache[table_name] ||= select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+        create_table_info_cache[table_name] ||= select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
       end
 
       def create_table_definition(name, temporary = false, options = nil, as = nil) # :nodoc: