Quote primary key in the subselect generated by mysql2 adapter

Otherwise it will occur syntax error if primary key is a reserved word.

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -717,7 +717,8 @@ module ActiveRecord
           # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
           subselect.distinct unless select.limit || select.offset || select.orders.any?
 
-          Arel::SelectManager.new(subselect.as("__active_record_temp")).project(Arel.sql(key.name))
+          key_name = quote_column_name(key.name)
+          Arel::SelectManager.new(subselect.as("__active_record_temp")).project(Arel.sql(key_name))
         end
 
         def supports_rename_index?

activerecord/test/cases/reserved_word_test.rb

@@ -39,7 +39,7 @@ class ReservedWordTest < ActiveRecord::TestCase
       t.string :order
       t.belongs_to :select
     end
-    @connection.create_table :values, force: true do |t|
+    @connection.create_table :values, primary_key: :as, force: true do |t|
       t.belongs_to :group
     end
   end
@@ -88,6 +88,13 @@ class ReservedWordTest < ActiveRecord::TestCase
     assert_equal x, Group.find(x.id)
   end
 
+  def test_delete_all_with_subselect
+    create_test_fixtures :values
+    assert_equal 1, Values.order(:as).limit(1).offset(1).delete_all
+    assert_raise(ActiveRecord::RecordNotFound) { Values.find(2) }
+    assert Values.find(1)
+  end
+
   def test_has_one_associations
     create_test_fixtures :group, :values
     v = Group.find(1).values

activerecord/test/fixtures/reserved_words/values.yml

@@ -1,7 +1,7 @@
 values1:
-  id: 1
+  as: 1
   group_id: 2
 
 values2:
-  id: 2
+  as: 2
   group_id: 1