MySQL的CAST函数用法

CREATE TABLE `tmp` (

  `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`;

参考：http://hongmin118.iteye.com/blog/2029728