mysql中实现触发器修改数据就添加一条记录到另一张表

创建一张表,填入数据：

CREATE DATABASE `test`;

USE `test`;

DROP TABLE IF EXISTS `tt`;

CREATE TABLE `tt` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `num` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

insert  into `tt`(`id`,`num`) values (1,4),(2,2),(3,3),(4,1);

创建一张日志表:
CREATE TABLE `log` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `effect` int(20) NOT NULL comment '受影响的行id',
  `created_time` datetime NOT NULL comment '创建时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

创建触发器:

DELIMITER $$

USE `test`$$

DROP TRIGGER  `trigger_tt`$$

CREATE

    TRIGGER `trigger_tt` AFTER UPDATE ON `tt` 
    FOR EACH ROW BEGIN
	IF((old.num != new.num) OR (old.num IS NULL && new.num IS NOT NULL))
	THEN
	
	INSERT `test`.`log` (`effect`,`created_time`) VALUES (new.id,NOW());
	
	END IF;
    END;
$$

DELIMITER ;

修改数据num之后向log表中写入一条数据

执行下面的语句进行测试:

UPDATE tt SET `num`=2 WHERE id =1;
UPDATE tt SET `num`=4 WHERE id =1;
UPDATE tt SET `num`=1 WHERE id =4;

查看log表数据
id   effect   created_time
1    1        2020-05-09 13:46:19
2    1        2020-05-09 13:46:50
3    4        2020-05-09 13:47:22