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mysql触发器之创建使用触发器简单示例

luyaran 人气:0
这篇文章主要介绍了mysql触发器之创建使用触发器,结合实例形式分析了mysql创建、查看、调用触发器的相关操作技巧,需要的朋友可以参考下

本文实例讲述了mysql触发器之创建使用触发器。分享给大家供大家参考,具体如下:

我们可以可以使用CREATE TRIGGER语句创建一个新的触发器,来看下具体的语法:

CREATE TRIGGER trigger_name trigger_time trigger_event
 ON table_name
 FOR EACH ROW
 BEGIN
 ...
 END;

然后我们来详细看下上述sql的具体含义:

大概了解了之后,我们就来尝试创建触发器来记录employees表中行数据的更改情况,先来看下这个表的结构:

mysql> DESC employees;
+----------------+--------------+------+-----+---------+-------+
| Field     | Type     | Null | Key | Default | Extra |
+----------------+--------------+------+-----+---------+-------+
| employeeNumber | int(11)   | NO  | PRI | NULL  |    |
| lastName    | varchar(50) | NO  |   | NULL  |    |
| firstName   | varchar(50) | NO  |   | NULL  |    |
| extension   | varchar(10) | NO  |   | NULL  |    |
| email     | varchar(100) | NO  |   | NULL  |    |
| officeCode   | varchar(10) | NO  | MUL | NULL  |    |
| reportsTo   | int(11)   | YES | MUL | NULL  |    |
| jobTitle    | varchar(50) | NO  |   | NULL  |    |
+----------------+--------------+------+-----+---------+-------+
8 rows in set

我们再来创建一个名为employees audit的新表,用来保存employees表中数据的更改:

CREATE TABLE employees_audit (
  id INT AUTO_INCREMENT PRIMARY KEY,
  employeeNumber INT NOT NULL,
  lastname VARCHAR(50) NOT NULL,
  changedat DATETIME DEFAULT NULL,
  action VARCHAR(50) DEFAULT NULL
);

再来创建一个BEFORE UPDATE触发器,该触发器在对employees表中的行记录更改之前被调用:

DELIMITER $$
CREATE TRIGGER before_employee_update 
  BEFORE UPDATE ON employees
  FOR EACH ROW 
BEGIN
  INSERT INTO employees_audit
  SET action = 'update',
   employeeNumber = OLD.employeeNumber,
    lastname = OLD.lastname,
    changedat = NOW(); 
END$$
DELIMITER ;

在上述触发器的主体中,我们使用OLD关键字来访问受触发器影响的行的employeeNumber和lastname列。我们要注意的是,在为insert定义的触发器中,可以仅使用NEW关键字。不能使用OLD关键字。但是,在为DELETE定义的触发器中,没有新行,因此您只能使用OLD关键字。在update触发器中,OLD是指更新前的行,而NEW是更新后的行。

然后,我们可以使用SHOW TRIGGERS语句,来查看数据库中的触发器:

mysql> SHOW TRIGGERS;
+------------------------+--------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| Trigger        | Event | Table   | Statement                                                                               | Timing | Created        | sql_mode                                     | Definer    | character_set_client | collation_connection | Database Collation |
+------------------------+--------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| before_employee_update | UPDATE | employees | BEGIN
  INSERT INTO employees_audit
  SET action = 'update',
   employeeNumber = OLD.employeeNumber,
    lastname = OLD.lastname,
    changedat = NOW();
END | BEFORE | 2017-08-02 22:06:36.40 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | root@localhost | utf8         | utf8_general_ci   | utf8_general_ci  |
+------------------------+--------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
1 row in set

完事我们就来更新employees表以检查触发器是否被调用:

UPDATE employees 
SET 
  lastName = 'Maxsu'
WHERE
  employeeNumber = 1056;

可以使用以下查询来查询employees_audit表,用以检查触发器是否被UPDATE语句调用:

mysql> SELECT * FROM employees_audit;
+----+----------------+----------+---------------------+--------+
| id | employeeNumber | lastname | changedat      | action |
+----+----------------+----------+---------------------+--------+
| 1 |      1056 | Hill   | 2017-08-02 22:15:51 | update |
+----+----------------+----------+---------------------+--------+
1 row in set

如上面输出结果所示,触发器被真正调用,并在employees_audit表中插入一个新行。

好啦,本次记录就到这里了。

希望本文所述对大家MySQL数据库计有所帮助。

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