MySQL 触发器示例

简介：

MySQL 触发器

这次实验是在一台 MySQL Slave 上进行的，事实证明：从库添加数据库、表、插入、删除数据等，不会导致主从失败。

一、创建实验数据库、表

mysql > create database trdb default character set utf8;

mysql > create table trdb.t_film (id int(5) primary key auto_increment, name varchar(32), cid int(3), status int(1));

mysql > desc trdb.t_film;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(5)      | NO   | PRI | NULL    | auto_increment |
| name   | varchar(32) | YES  |     | NULL    |                |
| cid    | int(3)      | YES  |     | NULL    |                |
| status | int(1)      | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+

mysql > create table trdb.t_tr (id int(5) primary key auto_increment, vid int(5), opertion int(1));

mysql > desc trdb.t_tr;
+----------+--------+------+-----+---------+----------------+
| Field    | Type   | Null | Key | Default | Extra          |
+----------+--------+------+-----+---------+----------------+
| id       | int(5) | NO   | PRI | NULL    | auto_increment |
| vid      | int(5) | YES  |     | NULL    |                |
| opertion | int(1) | YES  |     | NULL    |                |
+----------+--------+------+-----+---------+----------------+

# 表一：t_film 为业务数据表，执行 INSERT、UPDATE、DELETE 操作
# 表二：t_tr 为触发器程序体数据写入表

二、创建触发器

mysql > use trdb;

mysql > delimiter $

# 定义界定符，默认 ;

1、INSERT 事件

mysql > create trigger tr_insert after insert on t_film for each row
    -> begin
    -> if new.cid in (2, 3, 4, 5, 6, 45) then
    ->     insert into t_tr set vid = new.id, opertion = 1;
    -> end if;
    -> end$

# 语法介绍：
# 创建一个触发器，名为 tr_insert
# 触发时机，事件发生前 before、事件发生后 after
# 事件类型，insert、update、delete
# 为哪张表创建触发器，t_film ( 同一张表不能同时创建相同类型的触发器 )
# 触发器执行间隔，row 每行触发一次
# begin ... end，区域内可以写逻辑、多条SQL语句

begin
declare uid int(11);
set uid = (select uid from table where uid = new.uid);
if new.uid = uid then
    insert into trdb.tr_t set vid = new.fid, opertion = 1;
end if;
end$

# 变量赋值
# NEW、OLD
# INSERT 触发器时，NEW 表示 BEFORE 将要或 AFTER 已经插入的新数据
# UPDATE 触发器时，OLD 表示 BEFORE 将要或 AFTER 已经被修改的原数据，NEW 表示 BEFORE 将要或 AFTER 已经被修改为的新数据
# DELETE 触发器时，OLD 表示 BEFORE 将要或 AFTER 已经被删除的原数据

2、UPDATE 事件

mysql > create trigger tr_update after update on t_film for each row
    -> begin
    -> if new.cid in (2, 3, 4, 5, 6, 45) then
    ->     insert into t_tr set vid = new.id, opertion = 2;
    -> end if;
    -> end$

3、DELETE 事件

mysql > create trigger tr_delete after delete on t_film for each row
    -> begin
    -> if old.cid in (2, 3, 4, 5, 6, 45) then
    ->     insert into t_tr set vid = old.id, opertion = 3;
    -> end if;
    -> end$

mysql > delimiter ;

4、查看触发器

mysql > show triggers\G
*************************** 1. row ***************************
             Trigger: tr_insert
               Event: INSERT
               Table: t_film
           Statement: begin
if new.cid in (2, 3, 4, 5, 6, 45) then
    insert into t_tr set vid = new.id, opertion = 1;
end if;
end
              Timing: AFTER
             Created: NULL
            sql_mode:
             Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci
*************************** 2. row ***************************
             Trigger: tr_update
               Event: UPDATE
               Table: t_film
           Statement: begin
if new.cid in (2, 3, 4, 5, 6, 45) then
    insert into t_tr set vid = new.id, opertion = 2;
end if;
end
              Timing: AFTER
             Created: NULL
            sql_mode:
             Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci
*************************** 3. row ***************************
             Trigger: tr_delete
               Event: DELETE
               Table: t_film
           Statement: begin
if old.cid in (2, 3, 4, 5, 6, 45) then
    insert into t_tr set vid = old.id, opertion = 3;
end if;
end
              Timing: AFTER
             Created: NULL
            sql_mode:
             Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci

三、验证触发器

mysql > select * from t_film;
Empty set (0.00 sec)

mysql > select * from t_tr;
Empty set (0.00 sec)

1、INSERT 事件验证

mysql > insert into t_film set name = '警察故事 1', cid = 2, status = 1;

mysql > select * from t_film;
+----+----------------+------+--------+
| id | name           | cid  | status |
+----+----------------+------+--------+
|  1 | 警察故事 1     |    2 |      1 |
+----+----------------+------+--------+

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
+----+------+----------+

# 触发器达到效果，数据被写入

mysql > insert into t_film set name = '警察故事 2', cid = 41, status = 0;

mysql > select * from t_film;
+----+----------------+------+--------+
| id | name           | cid  | status |
+----+----------------+------+--------+
|  1 | 警察故事 1     |    2 |      1 |
|  2 | 警察故事 2     |   41 |      0 |
+----+----------------+------+--------+

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
+----+------+----------+

# 触发器达到效果，数据没有被写入，因为 cid not in (2, 3, 4, 5, 6, 45)

2、UPDATE 事件验证

mysql > update t_film set cid = 2, status = 1 where name = '警察故事 2';

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
|  2 |    2 |        2 |
+----+------+----------+

# 触发器达到效果，数据被写入

3、DELETE 事件验证

mysql > insert into t_film set name = '警察故事 3', cid = 41, status = 0;

mysql > select * from t_film;
+----+----------------+------+--------+
| id | name           | cid  | status |
+----+----------------+------+--------+
|  1 | 警察故事 1     |    2 |      1 |
|  2 | 警察故事 2     |    2 |      1 |
|  3 | 警察故事 3     |   41 |      0 |
+----+----------------+------+--------+

mysql > delete from t_film where name = '警察故事 1';

mysql > delete from t_film where name = '警察故事 3';

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
|  2 |    2 |        2 |
|  3 |    1 |        3 |
+----+------+----------+

# 触发器达到效果，只有删除 警察故事 1 的事件被记录

4、批量操作

mysql > select * from t_film;
+----+----------------+------+--------+
| id | name           | cid  | status |
+----+----------------+------+--------+
|  2 | 警察故事 2     |    2 |      1 |
|  4 | 警察故事 3     |   41 |      0 |
|  5 | 警察故事 4     |   41 |      0 |
|  6 | 警察故事 5     |   41 |      0 |
|  7 | 警察故事 6     |   41 |      0 |
|  8 | 警察故事 7     |   41 |      0 |
|  9 | 警察故事 8     |   41 |      0 |
| 10 | 警察故事 9     |   41 |      0 |
+----+----------------+------+--------+

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
|  2 |    2 |        2 |
|  3 |    1 |        3 |
+----+------+----------+

mysql > update t_film set cid = 2, status = 1 where cid = 41;

mysql > select * from t_tr;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
|  1 |    1 |        1 |
|  2 |    2 |        2 |
|  3 |    1 |        3 |
|  4 |    4 |        2 |
|  5 |    5 |        2 |
|  6 |    6 |        2 |
|  7 |    7 |        2 |
|  8 |    8 |        2 |
|  9 |    9 |        2 |
| 10 |   10 |        2 |
+----+------+----------+

mysql > delete from t_film;

mysql > select * from t_tr where id > 10;
+----+------+----------+
| id | vid  | opertion |
+----+------+----------+
| 11 |    2 |        3 |
| 12 |    4 |        3 |
| 13 |    5 |        3 |
| 14 |    6 |        3 |
| 15 |    7 |        3 |
| 16 |    8 |        3 |
| 17 |    9 |        3 |
| 18 |   10 |        3 |
+----+------+----------+

# 批量操作也没有问题！