Fixed #29480 -- Made MySQL backend retrieve constraint columns in their defined order.

django/db/backends/mysql/introspection.py

@@ -160,6 +160,7 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
             WHERE
                 kc.table_schema = DATABASE() AND
                 kc.table_name = %s
+            ORDER BY kc.`ordinal_position`
         """
         cursor.execute(name_query, [table_name])
         for constraint, column, ref_table, ref_column in cursor.fetchall():