Merge pull request rails#37465 from alpaca-tc/optimize_primary_keys

Fixed performance regression introduced MySQL 8.0

Author: kamipo

activerecord/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Fixed the performance regression for `primary_keys` introduced MySQL 8.0.
+
+    *Hiroyuki Ishii*
+
 *   `insert`, `insert_all`, `upsert`, and `upsert_all` now clear the query cache.
 
     *Eugene Kenny*

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -440,11 +440,11 @@ def primary_keys(table_name) # :nodoc:
 
         query_values(<<~SQL, "SCHEMA")
           SELECT column_name
-          FROM information_schema.key_column_usage
-          WHERE constraint_name = 'PRIMARY'
+          FROM information_schema.statistics
+          WHERE index_name = 'PRIMARY'
             AND table_schema = #{scope[:schema]}
             AND table_name = #{scope[:name]}
-          ORDER BY ordinal_position
+          ORDER BY seq_in_index
         SQL
       end