1 files changed, 26 insertions, 5 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 37e4eb24a8..0615e646b1 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -623,6 +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
 
@@ -772,6 +773,21 @@ module ActiveRecord
         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
@@ -951,11 +967,13 @@ 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?
@@ -1018,9 +1036,12 @@ 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: