mysql触发器实践

触发器(trigger)：监视某种情况，并触发某种操作。

触发器创建语法四要素：

1.监视地点(table)

2.监视事件(insert/update/delete)

3.触发时间(after/before)

4.触发事件(insert/update/delete)

语法：

create trigger triggerName

after/before insert/update/delete on 表名

for each row #这句话在mysql是固定的

begin

sql语句;

end;

举例说明：

创建两个表

[code]DROP TABLE IF EXISTS `t_a`;
CREATE TABLE `t_a` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

DROP TABLE IF EXISTS `t_b`;
CREATE TABLE `t_b` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

创建两个触发器：

(1)在t_a插入数据后，往t_b同步数据

[code]DROP TRIGGER
IF EXISTS t_afterinsert_on_ta;
CREATE TRIGGER t_afterinsert_on_ta 
AFTER INSERT ON t_a 
FOR EACH ROW
BEGIN
 INSERT INTO t_b (name)
VALUES
 (new.name);
END;

(1)在t_a删除数据后，删除t_b的对应数据​

[code]DROP TRIGGER
IF EXISTS t_afterdelete_on_ta;
CREATE TRIGGER t_afterdelete_on_ta 
AFTER DELETE ON t_a 
FOR EACH ROW
BEGIN
  delete from t_b where id = old.id;
END;
​

insert into t_a(name) value(‘liuyanliang’);

SELECT * from t_a

SELECT * from t_b

//发现t_a和t_b插入了一条相同的数据

DELETE FROM t_a where id = 1;

SELECT * from t_a

SELECT * from t_b

​

//发现t_a和t_b的数据都删除了

​