MySQL TIMESTAMP column with CURRENT_TIMESTAMP

在部署程序时遇到的一个问题,MySQL定义举例如下:

CREATE TABLE `example` (
  `id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
  `created` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `lastUpdated` TIMESTAMP NOT NULL ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;

这段SQL是我从项目中摘取出来的,在测试机器上一切正常,但是部署到生产机器上MySQL报错:

ERROR 1293 (HY000): Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause.

意思是只能有一个带CURRENT_TIMESTAMP的timestamp列存在,但是为什么本地测试却没有任何问题呢,本地测试的机器安装的MySQL版本5.6.13,而生产机器上安装的却是5.5版本,搜索网络后得知这两种版本之间对于timestamp处理的区别在于:

在MySQL 5.5文档有这么一段话:

One TIMESTAMP column in a table can have the current timestamp as the default value for initializing the column, as the auto-update value, or both. It is not possible to have the current timestamp be the default value for one column and the auto-update value for another column.

而在MySQL 5.6.5做出了以下改变:

Previously, at most one TIMESTAMP column per table could be automatically initialized or updated to the current date and time. This restriction has been lifted. Any TIMESTAMP column definition can have any combination of DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses. In addition, these clauses now can be used with DATETIME column definitions. For more information, see Automatic Initialization and Updating for TIMESTAMP and DATETIME.

根据网上的解决方案,可以使用触发器来替代一下:

CREATE TABLE `example` (
  `id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
  `created` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `lastUpdated` DATETIME NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB;
DROP TRIGGER IF EXISTS `update_example_trigger`;
DELIMITER //
CREATE TRIGGER `update_example_trigger` BEFORE UPDATE ON `example`
 FOR EACH ROW SET NEW.`lastUpdated` = NOW()
//
DELIMITER ;

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