MySQL的CAST函数用法

`id` int(11) NOT NULL AUTO_INCREMENT,
`test_value` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

CREATE TABLE `tmp1` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`value_int` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

INSERT INTO tmp1 SELECT
id,
CAST(test_value AS UNSIGNED) - 1
FROM
`tmp`;