转载地址:http://www.2cto.com/database/201212/176781.html
触发器是MySQL响应以下任意语句而自动执行的一条MySQL语句(或位于BEGIN和END语句之间的一组语句): www.2cto.com
DELETE;
INSERT;
UPDATE;
使用触发器,需要MySQL5或之后的版本支持。
一、触发器基本操作
1、创建触发器
创建触发器时,需要给出4条信息:
唯一的触发器名;(虽然MySQL5允许不同的表上的触发器名称相同,但一般最好不要这么做。)
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触发器关联的表;
触发器响应的事件;
触发器何时执行;
语法结构:
create trigger trigger_name (BEFORE|AFTER)
(delete|update|insert) on table_name
for each row
BEGIN
要触发的sql语句;
END;
示例:
[sql]
mysql> create trigger t_trig before insert on t_goods for each row
-> begin
-> set NEW.add_date = current_date();
-> end;
-> |
mysql> delimiter ;
mysql> insert into t_goods(id,goods_name,quantity)
-> values(1,‘apple‘,50);
-> |
mysql> select * from t_goods;
-> |
+------+------------+----------+------------+
| id | goods_name | quantity | add_date |
+------+------------+----------+------------+
| 1 | apple | 50 |
2012-12-12 |
+------+------------+----------+------------+
2、删除触发器
DROP TRIGGER [schema_name.]trigger_name;
示例:
mysql> DROP TRIGGER t_trig;
3、查看触发器
SHOW TRIGGERS [ FROM DBNAME [ like ‘‘ ]
];
示例:
[sql] www.2cto.com
mysql> show triggers;
+---------+--------+---------+------------------------------------------------------------------------------------------
| Trigger | Event | Table | Statement
+---------+--------+---------+------------------------------------------------------------------------------------------
| t_trig | INSERT | t_goods | begin
set NEW.add_date = current_date();
end | BEFORE | NULL | |
root@localhost | latin1 |
latin1_swedish_ci | latin1_swedish_ci |
+---------+--------+---------+------------------------------------------------------------------------------------------
mysql> show triggers from test;
+---------+--------+---------+------------------------------------------------------------------------------------------
| Trigger | Event | Table | Statement
+---------+--------+---------+------------------------------------------------------------------------------------------
| t_trig | INSERT | t_goods | begin
set NEW.add_date = current_date();
end | BEFORE | NULL | |
root@localhost | latin1 |
latin1_swedish_ci | latin1_swedish_ci |
+---------+--------+---------+------------------------------------------------------------------------------------------
mysql> show triggers from test like ‘t%‘;
+---------+--------+---------+------------------------------------------------------------------------------------------
| Trigger | Event | Table | Statement
+---------+--------+---------+------------------------------------------------------------------------------------------
| t_trig | INSERT | t_goods | begin
set NEW.add_date = current_date();
end | BEFORE | NULL | |
root@localhost | latin1 |
latin1_swedish_ci | latin1_swedish_ci |
+---------+--------+---------+------------------------------------------------------------------------------------------
二、注意事项
1、只有表支持触发器,视图及临时表都不支持;
2、每个表最多支持6个触发器;
3、单一触发器不能与多个事件或多个表关联;
4、对于INSERT而言,新增的行用NEW来表示,行中的每一列的值,用NEW.列名来表示;
对于DELETE而言,删除的行用OLD来表示;
对于UPDATE而言,更新前的行用OLD来表示,更新后的行用NEW来表示
【转】MYSQL入门学习之十一:触发器的基本操作,古老的榕树,5-wow.com