MySQL触发器 - 技术栈

一、简介

MySQL触发器和存储过程类似，都是可以在MySQL执行的一段程序。触发器是由事件来触发的，这些事件包括INSERT、UPDATE、DELETE语句。如果定义了触发器，当数据库执行这些语句的时候，就会执行触发器的程序。

触发器(trigger)是一个特殊的存储过程，不同的是，存储过程需要使用CALL语句来调用，而触发器的执行不需要使用CALL语句来调用，也不需要手工启动。而是通过定义SQL语句调用的事件来触发。触发器可以查询其他表，也可以执行复杂的SQL语句。

二、创建触发器

1.创建只有一个执行语句的触发器

CREATE TRIGGER trigger_name trigger_time trigger_event ON tbl_name FOR EACH ROW trigger_stmt

trigger_name：触发器名称
trigger_time：触发时机，可以指定为before或after
trigger_event：触发事件，包括INSERT、UPDATE、DELETE
tbl_name：建立触发器的表名，即在哪张表上建立触发器
trigger_stmt：触发器执行的语句

CREATE TABLE `fruits` (

`id` bigint NOT NULL AUTO_INCREMENT,

`number` varchar(255) DEFAULT NULL,

`name` varchar(255) DEFAULT NULL,

`price` double DEFAULT NULL,

PRIMARY KEY (`id`)

)

例：在fruits表创建一个触发器，计算器插入数据前，总的行数

mysql> CREATE TRIGGER sum_fruits_trigger BEFORE INSERT ON fruits FOR EACH ROW SET @sum =(select count(1) from fruits);//

Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO fruits (number, name, price) VALUES ('watermelon', '西瓜', 40);//

Query OK, 1 row affected (0.00 sec)

mysql> select @sum ;//

+------+

| @sum |

+------+

| 3 |

+------+

1 row in set (0.00 sec)

mysql> select * from fruits;//

+------+------------+--------+-------+

| id | number | name | price |

+------+------------+--------+-------+

| 10 | banana | 香蕉 | 20 |

| 1321 | apple | 苹果 | 100 |

| 1333 | watermelon | 西瓜 | 40 |

| 1334 | watermelon | 西瓜 | 40 |

+------+------------+--------+-------+

4 rows in set (0.00 sec)

可以看出在插入第四行之前，数据库中有3条记录，所以@sum返回3是正确的

2.创建有多个执行语句的触发器

CREARE TRIGGER trigger_name trigger_time trigger_event ON tbl_name FOR EACH ROW

BEGIN

trigger_stmt

END

trigger_name：触发器名称
trigger_time：触发时机，可以指定为before或after
trigger_event：触发事件，包括INSERT、UPDATE、DELETE
tbl_name：建立触发器的表名，即在哪张表上建立触发器
trigger_stmt：触发器执行的语句列表，可以是多个

例：创建一个触发器，在插入一条数据时，同时给其他多个表插入数据

sql 复制代码

CREATE TABLE test1 (a1 INT);
CREATE TABLE test2 (a2 INT);
CREATE TABLE test3 (a3 INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
CREATE TABLE test4 (a4 INT NOT NULL AUTO_INCREMENT PRIMARY KEY, b4 INT DEFAULT 0);

sql 复制代码

CREATE TRIGGER testMultiAdd BEFORE INSERT ON test1 FOR EACH ROW
BEGIN
    INSERT INTO test2 SET a2 = NEW.a1;
    DELETE FROM test3 WHERE a3 = NEW.a1;
    UPDATE test4 SET b4 = b4 +1 WHERE a4 = NEW.a1;
END;//

mysql> INSERT INTO test3 (a3) VALUES (NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL);

-> INSERT INTO test4 (a4) VALUES (0),(0),(0),(0),(0),(0),(0),(0),(0),(0);

-> //

Query OK, 8 rows affected (0.00 sec)

Records: 8 Duplicates: 0 Warnings: 0

Query OK, 10 rows affected (0.00 sec)

Records: 10 Duplicates: 0 Warnings: 0
mysql> INSERT INTO test1 VALUES (1),(3),(1),(7),(1),(8),(4),(4);//

Query OK, 8 rows affected (0.01 sec)

Records: 8 Duplicates: 0 Warnings: 0
mysql> SELECT * from test1;

+------+

| a1 |

+------+

| 1 |

| 3 |

| 1 |

| 7 |

| 1 |

| 8 |

| 4 |

| 4 |

+------+

8 rows in set (0.00 sec)

mysql> SELECT * from test2;

+------+

| a2 |

+------+

| 1 |

| 3 |

| 1 |

| 7 |

| 1 |

| 8 |

| 4 |

| 4 |

+------+

8 rows in set (0.01 sec)

mysql> SELECT * from test3;

+----+

| a3 |

+----+

| 2 |

| 5 |

| 6 |

+----+

3 rows in set (0.00 sec)

mysql> SELECT * from test4;

+----+------+

| a4 | b4 |

+----+------+

| 1 | 3 |

| 2 | 0 |

| 3 | 1 |

| 4 | 2 |

| 5 | 0 |

| 6 | 0 |

| 7 | 1 |

| 8 | 1 |

| 9 | 0 |

| 10 | 0 |

+----+------+

10 rows in set (0.00 sec)

从结果看，向表test1插入数据时，test2、test3、test4都发生了变化，证明触发器执行了。

三、查看触发器

1.使用SHOW TRIGGERS查看触发器状态信息

SHOW TRIGGERS;

查看所有的触发器

mysql> SHOW TRIGGERS\G

*************************** 1. row ***************************

Trigger: sum_fruits_trigger

Event: INSERT

Table: fruits

Statement: SET @sum =(select count(1) from fruits)

Timing: BEFORE

Created: 2024-06-29 15:27:18.99

sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

Definer: root@localhost

character_set_client: utf8mb4

collation_connection: utf8mb4_0900_ai_ci

Database Collation: utf8mb4_0900_ai_ci

*************************** 2. row ***************************

Trigger: testMultiAdd

Event: INSERT

Table: test1

Statement: BEGIN

INSERT INTO test2 SET a2 = NEW.a1;

DELETE FROM test3 WHERE a3 = NEW.a1;

UPDATE test4 SET b4 = b4 +1 WHERE a4 = NEW.a1;

END

Timing: BEFORE

Created: 2024-06-29 15:50:10.12

sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

Definer: root@localhost

character_set_client: utf8mb4

collation_connection: utf8mb4_0900_ai_ci

Database Collation: utf8mb4_0900_ai_ci

2 rows in set (0.00 sec)

注：这里\G意思是将输出结果从横向转换为纵向的

2.在triggers表中查看触发信息

SELECT * FROM INFORMATION_SCHEMA.TRIGGERS WHERE condition;

例如，查看名称为testMultiAdd的触发器

mysql> SELECT * FROM INFORMATION_SCHEMA.TRIGGERS WHERE TRIGGER_NAME = 'testMultiAdd'\G

*************************** 1. row ***************************

TRIGGER_CATALOG: def

TRIGGER_SCHEMA: dh_sys

TRIGGER_NAME: testMultiAdd

EVENT_MANIPULATION: INSERT

EVENT_OBJECT_CATALOG: def

EVENT_OBJECT_SCHEMA: dh_sys

EVENT_OBJECT_TABLE: test1

ACTION_ORDER: 1

ACTION_CONDITION: NULL

ACTION_STATEMENT: BEGIN

INSERT INTO test2 SET a2 = NEW.a1;

DELETE FROM test3 WHERE a3 = NEW.a1;

UPDATE test4 SET b4 = b4 +1 WHERE a4 = NEW.a1;

END

ACTION_ORIENTATION: ROW

ACTION_TIMING: BEFORE

ACTION_REFERENCE_OLD_TABLE: NULL

ACTION_REFERENCE_NEW_TABLE: NULL

ACTION_REFERENCE_OLD_ROW: OLD

ACTION_REFERENCE_NEW_ROW: NEW

CREATED: 2024-06-29 15:50:10.12

SQL_MODE: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

DEFINER: root@localhost

CHARACTER_SET_CLIENT: utf8mb4

COLLATION_CONNECTION: utf8mb4_0900_ai_ci

DATABASE_COLLATION: utf8mb4_0900_ai_ci

1 row in set (0.00 sec)

四、删除触发器

DROP TRIGGER [schema_name.]trigger_name

DROP TRIGGER：删除触发器关键字
schema_name：表示数据库名称，可选，如果省略了表示行当前数据库删除
trigger_name：触发器名

mysql> DROP TRIGGER sum_fruits_trigger;

Query OK, 0 rows affected (0.01 sec)

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