CREATE TABLE t1 (f1 ENUM('', 'one', 'two'), KEY (f1)) ENGINE=InnoDB;
INSERT INTO t1 VALUES ('');
INSERT INTO t1 VALUES ('one'), ('two');
INSERT INTO t1 VALUES (0), (1), (2);
Warnings:
Warning	1265	Data truncated for column 'f1' at row 1
SELECT COUNT(*) = 6 FROM t1;
COUNT(*) = 6
1
SELECT COUNT(*) = 2 FROM t1 where f1 = '';
COUNT(*) = 2
1
SELECT COUNT(*) = 2 FROM t1 where f1 = 'one';
COUNT(*) = 2
1
DROP TABLE t1;
CREATE TABLE t1 (f1 ENUM('', 'one', 'two', 'three', 'four') PRIMARY KEY) ENGINE=InnoDB;
INSERT INTO t1 VALUES (''), ('one'), ('two');
SELECT COUNT(*) = 3 FROM t1;
COUNT(*) = 3
1
SELECT COUNT(*) = 1 FROM t1 WHERE f1 = '';
COUNT(*) = 1
1
SET AUTOCOMMIT=OFF;
START TRANSACTION;
UPDATE t1 SET f1 = 'three' where f1 = '';
SET AUTOCOMMIt=OFF;
START TRANSACTION;
UPDATE t1 SET f1 = 'four' where f1 = '';
COMMIT;
COMMIT;
ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
SELECT COUNT(*) = 1 FROM t1 WHERE f1 = 'three';
COUNT(*) = 1
1
DROP TABLE t1;