标签：arch new use 语法 0.00 baidu 晋级 http 情感
mysql表设计网址:王李-MySQL表设计
0.什么时候会用到触发器
百度解释:百度百科-触发器
个人理解:
触发器就是我们预先定义好的触发任务,当我们变动表的时候,正好符合触发器的规则,那就执行触发器。
1.触发器的格式
针对于DML触发器:
1 CREATE TRIGGER TRIGGER_NAME 2 BEFORE/ALTER INSERT/UPDATE/DELETE TB_NAME 3 FOR EACH NOW 4 BEGIN 5 ... 6 END
这里稍微解释一下:
1 1.触发器分为before和alter之分,before是在数据改变前,alter在数据改变后,最大的不同就是before可以改变new的值，而alter则不会 2 2.监视的动作也分为三种,INSERT UPDATE 和 DELETE ，意思是当表做这些动作的时候就执行下面的语句 3 3.for each now 就是每改变一行都会去检查一下触发器的条件 4 4.begin 这就意味着下面就是执行的语句了 5 5.end 这就意味着触发器结束了
贴几个关于mysql 触发器的教程:触发器教程
2.触发器的实际应用
修改MySQL默认执行结束符
1 delimiter $
关联文章:王李-MySQL表设计
2.1 实现功能:在增加b_book_information数据的时候,每增加一条,就会向表b_book_amount添加一行数据,数据的内容是书本编号和书本册书
1 mysql> create trigger t_insert_book_amount 2 -> after insert on b_book_information 3 -> for each row 4 -> begin 5 -> insert into b_book_amount (book_id,book_count) values (new.book_id,10); 6 -> end $ 7 Query OK, 0 rows affected (0.08 sec)
2.2 实现功能:我删除b_book_information数据的时候,会自动删除b_book_amount对应书本编号的数据
1 mysql> create trigger t_delete_book_amount 2 -> after delete on b_book_information 3 -> for each row 4 -> begin 5 -> delete from b_book_amount where book_id = old.book_id; 6 -> end$ 7 Query OK, 0 rows affected (0.06 sec)
2.3 每删除b_borrow_info表一条数据的时候,就会向b_book_amount添加该书本编号对应的册数,使其加1
1 mysql> create trigger t_delete_borrow 2 -> after delete on b_borrow_info 3 -> for each row 4 -> begin 5 -> update b_book_amount set book_count = book_count + 1 where book_id = old.book_id; 6 -> end$ 7 Query OK, 0 rows affected (0.06 sec)
3.检查触发器
2.1 检查
插入之前检查
1 mysql> select * from b_book_information where book_id = ‘d1112‘$ 2 Empty set (0.01 sec) 3 4 mysql> select * from b_book_amount where book_id = ‘d1112‘$ 5 Empty set (0.02 sec) 6 7 mysql>
插入数据
1 mysql> insert into b_book_information values (‘d1112‘,‘O1102‘,‘情感暴力‘,‘加藤谛三‘,19.00,‘哈佛大学心理导师情感自修课，优质畅销心理作品；别让你的爱变刀子，也被让他人的爱伤害你。停止心理"杀亲"，才能爱和被爱。‘)$ 2 Query OK, 1 row affected (0.11 sec)
插入之后检查
1 mysql> select * from b_book_information where book_id = ‘d1112‘$ 2 +---------+-------------+-----------+-------------+------------+----------------------------------------------------------------------------------------------------------------------+ 3 | book_id | category_id | book_name | book_author | book_price | book_remask | 4 +---------+-------------+-----------+-------------+------------+----------------------------------------------------------------------------------------------------------------------+ 5 | d1112 | O1102 | 情感暴力 | 加藤谛三 | 19.00 | 哈佛大学心理导师情感自修课，优质畅销心理作品；别让你的爱变刀子，也被让他人的爱伤害你。停止心理"杀亲"，才能爱和被爱。 | 6 +---------+-------------+-----------+-------------+------------+----------------------------------------------------------------------------------------------------------------------+ 7 1 row in set (0.02 sec) 8 9 mysql> select * from b_book_amount where book_id = ‘d1112‘$ 10 +---------+------------+ 11 | book_id | book_count | 12 +---------+------------+ 13 | d1112 | 10 | 14 +---------+------------+ 15 1 row in set (0.00 sec) 16 17 mysql>
2.2 检查
现在将删除2.1中添加的book_id为‘d1112‘的数据
1 mysql> delete from b_book_information where book_id = ‘d1112‘$ 2 Query OK, 1 row affected (0.04 sec)
删除之后查看数据
1 mysql> delete from b_book_information where book_id = ‘d1112‘$ 2 Query OK, 1 row affected (0.04 sec) 3 4 mysql> select * from b_book_information where book_id = ‘d1112‘$ 5 Empty set (0.00 sec) 6 7 mysql> select * from b_book_amount where book_id = ‘d1112‘$ 8 Empty set (0.00 sec) 9 10 mysql>
2.3 检查
查看未删除b_borrow_info之前的数据
1 mysql> select * from b_borrow_info where user_id = ‘D170117‘ and book_id = ‘d1101‘$ 2 +---------+---------+-------------+-------------+ 3 | user_id | book_id | create_date | update_date | 4 +---------+---------+-------------+-------------+ 5 | D170117 | d1101 | 2017-07-17 | NULL | 6 +---------+---------+-------------+-------------+ 7 1 row in set (0.00 sec) 8 9 mysql> select * from b_book_amount where book_id in (select book_id from b_borrow_info where user_id = ‘D170117‘ and book_id = ‘d1101‘) $ 10 +---------+------------+ 11 | book_id | book_count | 12 +---------+------------+ 13 | d1101 | 10 | 14 +---------+------------+ 15 1 row in set (0.01 sec) 16 17 mysql>
删除b_borrow_info的数据
1 mysql> delete from b_borrow_info where user_id = ‘D170117‘ and book_id = ‘d1101‘$ 2 Query OK, 1 row affected (0.06 sec)
删除之后查看
1 mysql> select * from b_borrow_info where user_id = ‘D170117‘ and book_id = ‘d1101‘$ 2 Empty set (0.00 sec) 3 4 mysql> select * from b_book_amount where book_id = ‘d1101‘$ 5 +---------+------------+ 6 | book_id | book_count | 7 +---------+------------+ 8 | d1101 | 11 | 9 +---------+------------+ 10 1 row in set (0.00 sec) 11 12 mysql>
4.注意事项
语法注意:
1 create trigger t_name 2 before/after insert/update/delete on tn_name 3 for each now 4 begin 5 ... 6 end
其中ON 和 begin 是初学者最容易忘记的
END
标签：arch new use 语法 0.00 baidu 晋级 http 情感
原文地址：http://www.cnblogs.com/wang-li/p/7215460.html
