DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a ENUM('5','6') CHARACTER SET BINARY);

INSERT INTO t1 VALUES ('5'),('6');

SELECT * FROM t1 WHERE a='5';

SELECT * FROM t1 WHERE a=1;

SELECT * FROM t1 WHERE CASE a WHEN 1 THEN 1 ELSE 0 END;

+------+

| a    |

+------+

| 5    |

+------+

SELECT * FROM t1 WHERE CASE a WHEN 1 THEN 1 ELSE 0 END AND a='5';

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a ENUM('a','b'));

INSERT INTO t1 VALUES ('a'),('b');

EXPLAIN EXTENDED SELECT * FROM t1 WHERE CASE a WHEN 'a' THEN 1 ELSE 0 END AND a='a';

SHOW WARNINGS;

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

| Level | Code | Message                                                                                                                              |

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

| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 'a') and (case `test`.`t1`.`a` when 'a' then 1 else 0 end)) |

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

SELECT * FROM t1 WHERE CASE 'a' WHEN 'a' THEN 1 ELSE 0 END AND a='a';

SELECT * FROM t1 WHERE a='a';