http://dev.mysql.com/doc/refman/5.7/en/type-conversion.html
When an operator is used with operands of different types, type conversion occurs to make the operands compatible. Some conversions occur implicitly. For example, MySQL automatically converts numbers to strings as necessary, and vice versa.
It is also possible to convert a number to a string explicitly using the CAST() function. Conversion occurs implicitly with the CONCAT() function because it expects string arguments.
1 SET FOREIGN_KEY_CHECKS=0; 2 3 -- ---------------------------- 4 -- Table structure for w1 5 -- ---------------------------- 6 DROP TABLE IF EXISTS `w1`; 7 CREATE TABLE `w1` ( 8 `id` int(11) NOT NULL AUTO_INCREMENT, 9 `wint` int(11) DEFAULT NULL, 10 PRIMARY KEY (`id`) 11 ) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin; 12 13 -- ---------------------------- 14 -- Records of w1 15 -- ----------------------------
1 INSERT INTO w1 (wint) VALUES ('www'); 2 INSERT INTO w1 (wint) VALUES ('wa'); 3 INSERT INTO w1 (wint) VALUES (123); 4 5 6 7 8 9 10 11 SET FOREIGN_KEY_CHECKS=0; 12 13 -- ---------------------------- 14 -- Table structure for w1 15 -- ---------------------------- 16 DROP TABLE IF EXISTS `w1`; 17 CREATE TABLE `w1` ( 18 `id` int(11) NOT NULL AUTO_INCREMENT, 19 `wint` int(11) DEFAULT NULL, 20 PRIMARY KEY (`id`) 21 ) ENGINE=MyISAM AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin; 22 23 -- ---------------------------- 24 -- Records of w1 25 -- ---------------------------- 26 INSERT INTO `w1` VALUES ('1', '0'); 27 INSERT INTO `w1` VALUES ('2', '0'); 28 INSERT INTO `w1` VALUES ('3', '123');