触发器的作用
触发器是自动化的SQL程序，由插入、更新和删除事件来触发。
当面对复杂的业务关系，在程序上难以实现时。
当程序上实现较为复杂，希望在数据库内实现时。
触发器的语法
CREATE TRIGGER <触发器名称>
{BEFORE|AFTER}
{INSERT |UPDATE |DELETE}
ON <表名称>
FOR EATH ROW
<触发器SQL语句>
创建简单的触发器
创建数据库
mysql> use db1;
ERROR 1049 (42000): Unknown database 'db1'
mysql> create database db1;
Query OK, 1 row affected (0.07 sec)
使用数据库
mysql> use db1;
Database changed
mysql> show tables;
Empty set (0.00 sec)
创建表
mysql> create table t1 ( id int, namevarchar(10), salary int );
Query OK, 0 rows affected (0.05 sec)
查看表结构
mysql> desc t1;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key |Default | Extra |
+--------+-------------+------+-----+---------+-------+
| id | int(11) | YES | |NULL | |
| name | varchar(10) | YES | | NULL | |
| salary | int(11) | YES | | NULL | |
+--------+-------------+------+-----+---------+-------+
3 rows in set (0.09 sec)
创建表
mysql> create table t2 (
-> user_total int,
-> salary_total int
-> );
Query OK, 0 rows affected (0.05 sec)
查看表结构
mysql> desc t2;
+--------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------+------+-----+---------+-------+
| user_total | int(11) | YES | |NULL | |
| salary_total | int(11) | YES | |NULL | |
+--------------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
插入数据
mysql> insert into t1 values (1,'jingjing',3000),
(2,'Lee',2000),
(3,'Tom',5000),
(4,'Lily',7000),
(5,'July',1000);
Query OK, 5 rows affected (0.03 sec)
Records: 5 Duplicates: 0 Warnings: 0
查看数据
mysql> select * from t1;
+------+----------+--------+
| id | name | salary |
+------+----------+--------+
| 1 | jingjing | 3000 |
| 2 | Lee | 2000 |
| 3 | Tom | 5000 |
| 4 | Lily | 7000 |
| 5 | July | 1000 |
+------+----------+--------+
5 rows in set (0.00 sec)
T2表插入数据
mysql> insert into t2 selectcount(*),sum(salary) from t1;
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 5 | 18000 |
+------------+--------------+
1 row in set (0.00 sec)
创建触发器
mysql> create trigger t1_ai after inserton t1 for each row update t2 set user_total=user_total+1,salary_total=salary_total+new.salary;
Query OK, 0 rows affected (0.02 sec)
mysql> select * from t1;
+------+----------+--------+
| id | name | salary |
+------+----------+--------+
| 1 | jingjing | 3000 |
| 2 | Lee | 2000 |
| 3 | Tom | 5000 |
| 4 | Lily | 7000 |
| 5 | July | 1000 |
+------+----------+--------+
5 rows in set (0.00 sec)
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 5 | 18000 |
+------------+--------------+
1 row in set (0.00 sec)
T1表增加了一条数据
mysql> insert into t1 values(6,'jack',2000);
Query OK, 1 row affected (0.00 sec)
T2表数据发生了变化。
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 6 | 20000 |
+------------+--------------+
1 row in set (0.00 sec)
创建触发器2
mysql> create trigger t1_ad
-> after delete on t1
-> for each row
-> update t2 set
-> user_total=user_total-1,
-> salary_total=salary_total-old.salary;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from t1;
+------+----------+--------+
| id | name | salary |
+------+----------+--------+
| 1 | jingjing | 3000 |
| 2 | Lee | 2000 |
| 3 | Tom | 5000 |
| 4 | Lily | 7000 |
| 5 | July | 1000 |
| 6 | jack | 2000 |
+------+----------+--------+
6 rows in set (0.00 sec)
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 6 | 20000 |
+------------+--------------+
1 row in set (0.00 sec)
删除一行数据
mysql> delete from t1 where id=6;
Query OK, 1 row affected (0.05 sec)
mysql> select * from t1;
+------+----------+--------+
| id | name | salary |
+------+----------+--------+
| 1 | jingjing | 3000 |
| 2 | Lee | 2000 |
| 3 | Tom | 5000 |
| 4 | Lily | 7000 |
| 5 | July | 1000 |
+------+----------+--------+
5 rows in set (0.00 sec)
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 5 | 18000 |
+------------+--------------+
1 row in set (0.00 sec)
创建触发器
mysql> create trigger t1_au after updateon t1 for each row update t2 set salary_total=salary_total-old.salary+new.salary;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from t1;
+------+----------+--------+
| id | name | salary |
+------+----------+--------+
| 1 | jingjing | 3000 |
| 2 | Lee | 2000 |
| 3 | Tom | 5000 |
| 4 | Lily | 7000 |
| 5 | July | 1000 |
+------+----------+--------+
5 rows in set (0.00 sec)
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 5 | 18000 |
+------------+--------------+
1 row in set (0.00 sec)
更新数据
mysql> update t1 set salary=2000 whereid=5;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
查看
mysql> select * from t2;
+------------+--------------+
| user_total | salary_total |
+------------+--------------+
| 5 | 19000 |
+------------+--------------+
1 row in set (0.00 sec)
同一个事件无法创建两个以上的触发器。
如果想创建两个可以用after和before的方式。
After update on T1 表示 T1更新之后触发T2。
Before update on T1表示T1更新之前触发T2。
事件和触发器影响的事件在同一个事物里面。因此不会出现数据不一致的情况。
创建多执行语句触发器
Begin和end
加入了判断语句，统称为流控制语句
使用IF语句的触发器1
mysql> create table t3 (
-> id int,
-> name varchar(10),
-> gid int
-> );
Query OK, 0 rows affected (0.04 sec)
mysql>
mysql>
mysql> create table t4 (
-> user_total int,
-> vip_total int
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> insert into t3 values
-> (1,'joe',0),
-> (2,'Ken',1),
-> (3,'Norman',0),
-> (4,'Tobb',0),
-> (5,'July',1),
-> (6,'Zen',1),
-> (7,'Bob',0),
-> (8,'Mars',1),
-> (9,'Tom',0),
-> (10,'Lee',0);
Query OK, 10 rows affected (0.04 sec)
Records: 10 Duplicates: 0 Warnings: 0
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
+------+--------+------+
10 rows in set (0.00 sec)
mysql> insert into t4 values (6,4);
Query OK, 1 row affected (0.00 sec)
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
+------+--------+------+
10 rows in set (0.00 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 6 | 4 |
+------------+-----------+
1 row in set (0.00 sec)
创建触发器
mysql> delimiter // 把SQL语句的结束符改成//
mysql> create trigger t3_ai
-> after insert on t3
-> for each row
-> if new.gid=0 then
-> update t4 set user_total=user_total+1;
-> else update t4 set vip_total=vip_total+1;
-> end if;
-> //
Query OK, 0 rows affected (0.01 sec)
mysql> delimiter ; 把SQL语句的结束符改为;
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
+------+--------+------+
10 rows in set (0.00 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 6 | 4 |
+------------+-----------+
1 row in set (0.00 sec)
更新数据
mysql> insert into t3 values(11,'jing',0);
Query OK, 1 row affected (0.01 sec)
查看
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
| 11 | jing | 0 |
+------+--------+------+
11 rows in set (0.00 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 7 | 4 |
+------------+-----------+
1 row in set (0.00 sec)
使用IF语句的触发器2
mysql> delimiter //
mysql>create trigger t3_ad after deleteon t3 for each row if old.gid=0 then update t4 set user_total=user_total-1; elseupdate t4 set vip_total=vip_total-1; end if;//
mysql> delimiter ;
使用IF语句的触发器3
mysql> delimiter //
mysql>create trigger t3_au after updateon t3 for each row if new.gid!=old.gid and new.gid=0 then update t4 setuser_total=user_total+1,vip_total=vip_total-1; else new.gid!=old.gid andnew.gid=1 then update t4 set user_total=user_total-1,vip_total=vip_total+1; endif;//
mysql> delimiter ;
使用CASE语句的触发器1
mysql> delimiter //
mysql>create trigger t3_au after updateon t3 for each row CASE WHEN new.gid!=old.gid and new.gid=0 then update t4 setuser_total=user_total+1,vip_total=vip_total-1; WHEN new.gid!=old.gid andnew.gid=1 then update t4 set user_total=user_total-1,vip_total=vip_total+1; endcase;//
mysql> delimiter ;
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
| 11 | jing | 0 |
+------+--------+------+
11 rows in set (0.01 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 7 | 4 |
+------------+-----------+
1 row in set (0.00 sec)
mysql> update t3 set gid=1 where id=11;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 6 | 5 |
+------------+-----------+
1 row in set (0.00 sec)
使用CASE语句的触发器2
mysql> delimiter //
mysql>create trigger t3_ad after deleteon t3 for each row CASE WHEN old.gid=0 then update t4 set user_total=user_total-1;WHEN old.gid=1 then update t4 set vip_total=vip_total-1; end case;//
mysql> delimiter ;
mysql> select * from t3;
+------+--------+------+
| id | name | gid |
+------+--------+------+
| 1 | joe | 0 |
| 2 | Ken | 1 |
| 3 | Norman | 0 |
| 4 | Tobb | 0 |
| 5 | July | 1 |
| 6 | Zen | 1 |
| 7 | Bob | 0 |
| 8 | Mars | 1 |
| 9 | Tom | 0 |
| 10 | Lee | 0 |
| 11 | jing | 1 |
+------+--------+------+
11 rows in set (0.00 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 6 | 5 |
+------------+-----------+
1 row in set (0.00 sec)
mysql> delete from t3 where id=11;
Query OK, 1 row affected (0.00 sec)
mysql> select * from t4;
+------------+-----------+
| user_total | vip_total |
+------------+-----------+
| 6 | 4 |
+------------+-----------+
1 row in set (0.00 sec)
使用loop语句的触发器1
每次选取一个随机值
mysql> select id,name,gid from t3 orderby rand() limit 1;
+------+------+------+
| id | name | gid |
+------+------+------+
| 6 | Zen | 1 |
+------+------+------+
1 row in set (0.00 sec)
T3表ID列加索引
mysql> alter table t3 add index (id);
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0
Rand()依然是全表扫描
mysql> explain select id,name,gid fromt3 order by rand() limit 1\G;
*************************** 1. row***************************
id: 1
select_type: SIMPLE
table: t3
partitions: NULL
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 10
filtered: 100.00
Extra: Using temporary; Using filesort
1 row in set, 1 warning (0.00 sec)
ERROR:
No query specified
创建表
mysql> create table t5 (
-> event_date date,
-> wnnum int
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> create table t6 (
-> id int,
-> name varchar(10),
-> gid int,
-> event_date date
-> );
Query OK, 0 rows affected (0.04 sec)
mysql> desc t5;
+------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default |Extra |
+------------+---------+------+-----+---------+-------+
| event_date | date | YES | | NULL | |
| wnnum | int(11) | YES | | NULL | |
+------------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> desc t6;
+------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key |Default | Extra |
+------------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(10) | YES | | NULL | |
| gid | int(11) | YES | |NULL | |
| event_date | date | YES | | NULL | |
+------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
触发器
mysql> create trigger t5_ai after inserton t5 for each row begin declare mnum int default 0;
-> declare wnum int;
-> declare tnum int;
-> declare rnum int;
-> declare tdate date;
-> select count(*) into tnum from t3;
-> set tdate=new.event_date;
-> set wnum=new.wnnum;
-> t5_loop:loop
-> set mnum=mnum+1;
-> set rnum=floor(1+rand()*tnum);
-> insert into t6 select id,name,gid,tdate from t3 where id=rnum;
-> if mnum>=wnum
-> then leave t5_loop;
-> end if;
-> end loop t5_loop;
-> end;
-> //
Query OK, 0 rows affected (0.01 sec)
查看
mysql> select * from t5;
Empty set (0.01 sec)
mysql> select * from t6;
Empty set (0.00 sec)
插入数据
mysql> insert into t5 values('2014-3-2',3);
Query OK, 1 row affected (0.12 sec)
查看t6表
mysql> select * from t6;
+------+--------+------+------------+
| id | name | gid | event_date |
+------+--------+------+------------+
| 2 | Ken | 1 | 2014-03-02 |
| 3 | Norman | 0 | 2014-03-02 |
| 7 | Bob | 0 | 2014-03-02 |
+------+--------+------+------------+
3 rows in set (0.00 sec)
使用Repeat语句的触发器1
mysql> create trigger t5_ai after inserton t5 for each row begin declare mnum int default 0;
-> declare wnum int;
-> declare tnum int;
-> declare rnum int;
-> declare tdate date;
-> select count(*) into tnum from t3;
-> set tdate=new.event_date;
-> set wnum=new.wnnum;
-> Repeat
-> Set mnum=mnum+1;
-> Set rnum=floor(1+rand()*tnum);
-> Insert into t6 select id,name,gid,tdate
-> From t3 where id=rnum;
-> Until mnum>=wnum
-> End repeat;
-> End;
-> //
此循环语句比LOOP简便。
使用while语句的触发器1
mysql> create trigger t5_ai after inserton t5 for each row begin declare mnum int default 0;
-> declare wnum int;
-> declare tnum int;
-> declare rnum int;
-> declare tdate date;
-> select count(*) into tnum from t3;
-> set tdate=new.event_date;
-> set wnum=new.wnnum;
-> while mnum<wnum
-> Set mnum=mnum+1;
-> Set rnum=floor(1+rand()*tnum);
-> Insert into t6 select id,name,gid,tdate
-> From t3 where id=rnum;
-> end while;
-> End;
-> //
While循环语句最简单
查看触发器
mysql> show triggers\G;
这种可以指定显示
mysql> select * frominformation_schema.triggers where TRIGGER_NAME='t1_ai'\G;
*************************** 1. row***************************
TRIGGER_CATALOG: def
TRIGGER_SCHEMA: db1
TRIGGER_NAME: t1_ai
EVENT_MANIPULATION: INSERT
EVENT_OBJECT_CATALOG: def
EVENT_OBJECT_SCHEMA: db1
EVENT_OBJECT_TABLE: t1
ACTION_ORDER: 1
ACTION_CONDITION: NULL
ACTION_STATEMENT: update t2 set user_total=user_total+1,salary_total=salary_total+new.salary
ACTION_ORIENTATION: ROW
ACTION_TIMING: AFTER
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
ACTION_REFERENCE_OLD_ROW: OLD
ACTION_REFERENCE_NEW_ROW: NEW
CREATED: 2016-01-2816:14:11.22
SQL_MODE:ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
DEFINER: root@localhost
CHARACTER_SET_CLIENT: utf8
COLLATION_CONNECTION: utf8_general_ci
DATABASE_COLLATION: latin1_swedish_ci
1 row in set (0.02 sec)
ERROR:
No query specified
删除触发器
Drop trigger trigger_name;
转载于:https://blog.51cto.com/sunshinesnail/1739862
