MySQL的触发器

一：概述

（1）介绍

（2）特性 

二：基本操作

-- 用户表
create table user(
     uid int primary key,
	 username varchar(50) not null,
	 password varchar(50) not null
);

-- 用户信息操作日志表
create table user_logs(
     id int primary key auto_increment,
	 time timestamp,
	 log_text varchar(255)
);

-- 需求1：当user表添加一行数据，则会自动在user_log添加日志记录
-- 定义触发器 trigger_test1
create trigger trigger_test1 after insert
on user for each row
insert into user_logs values(NULL,now(),'有新用户添加');

-- 在user表添加数据，让触发器自动执行
insert into user values(1,'张三','123456');


-- 需求2：当user表数据被修改时，则会自动在user_log添加日志记录
delimiter $$
create trigger trigger_test3 before update
on user for each row
begin
   insert into user_logs values(NULL,now(),'有用户信息被修改');
end $$
delimiter ;

-- 在user表修改数据，让触发器自动执行
update user set password = '888888' where uid = 1;

三：NEW和OLD

-- 删除触发器
drop trigger if exists trigger_test2;

-- NEW
-- 定义触发器：trigger_test3
drop trigger if exists trigger_test3;
create trigger trigger_test3 after insert
on user for each row
insert into user_logs values (NULL,now(),concat('有新用户添加，信息为：',NEW.uid,NEW.username,NEW.password));

insert into user values(5,'赵六','123456');


-- update类型的触发器
-- OLD
drop trigger if exists trigger_test4;
create trigger trigger_test4 after update
on user for each row
insert into user_logs values (NULL,now(),concat('有用户信息修改，修改前信息为：',OLD.uid,OLD.username,OLD.password));

update user set password = '999999'where uid = 4;

-- NEW
drop trigger if exists trigger_test5;
create trigger trigger_test5 after update
on user for each row
insert into user_logs values (NULL,now(),concat_ws(',','有用户信息修改，修改后信息为：',NEW.uid,NEW.username,NEW.password));

update user set password = '000000'where uid = 1;

-- delete类型的触发器
-- OLD
drop trigger if exists trigger_test6;
create trigger trigger_test6 after delete
on user for each row
insert into user_logs values (NULL,now(),concat_ws(',','有用户被删除，被删除用户信息为：',OLD.uid,OLD.username,OLD.password));

delete from user where uid = 5;

四：其他操作

五：注意事项