MariaDB [foo]> create table mdev_8026 (foo varchar(2), bar varchar(2), constraint foobar primary key (foo, bar));

Query OK, 0 rows affected (0.03 sec)

MariaDB [foo]> explain delete from mdev_8026 where foo='ab' and bar='cd';

+------+-------------+-----------+-------+---------------+---------+---------+------+------+-------------+

| id   | select_type | table     | type  | possible_keys | key     | key_len | ref  | rows | Extra       |

+------+-------------+-----------+-------+---------------+---------+---------+------+------+-------------+

|    1 | SIMPLE      | mdev_8026 | range | PRIMARY       | PRIMARY | 16      | NULL |    1 | Using where |

+------+-------------+-----------+-------+---------------+---------+---------+------+------+-------------+

1 row in set (0.00 sec)

MariaDB [foo]> explain delete from mdev_8026 where (foo, bar) = ('ab', 'cd');

+------+-------------+-----------+------+---------------+------+---------+------+------+-------------+

| id   | select_type | table     | type | possible_keys | key  | key_len | ref  | rows | Extra       |

+------+-------------+-----------+------+---------------+------+---------+------+------+-------------+

|    1 | SIMPLE      | mdev_8026 | ALL  | NULL          | NULL | NULL    | NULL |    1 | Using where |

+------+-------------+-----------+------+---------------+------+---------+------+------+-------------+

1 row in set (0.00 sec)