DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a DECIMAL, KEY(a)) ENGINE=MyISAM;

INSERT INTO t1 VALUES (1),(2),(3),(4),(5);

EXPLAIN SELECT * FROM t1 WHERE a='ax' ORDER BY a;

SHOW WARNINGS;

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

| Level   | Code | Message                                               |

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

| Warning | 1366 | Incorrect decimal value: 'ax' for column 'a' at row 1 |

| Warning | 1366 | Incorrect decimal value: 'ax' for column 'a' at row 1 |

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