MySQL/MariaDB数据库的触发器

　　　　　　　　　　MySQL/MariaDB数据库的触发器

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　作者：尹正杰

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一.触发器概述

1>.什么是触发器

　　触发器的执行不是由程序调用，也不是由手工启动，而是由事件来触发、激活从而实现执行。=

2>.创建触发器帮助信息

MariaDB [yinzhengjie]> HELP CREATE TRIGGER
Name: 'CREATE TRIGGER'
Description:
Syntax:
CREATE
    [DEFINER = { user | CURRENT_USER }]
    TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW trigger_body

This statement creates a new trigger. A trigger is a named database
object that is associated with a table, and that activates when a
particular event occurs for the table. The trigger becomes associated
with the table named tbl_name, which must refer to a permanent table.
You cannot associate a trigger with a TEMPORARY table or a view.

CREATE TRIGGER requires the TRIGGER privilege for the table associated
with the trigger. The statement might also require the SUPER privilege,
depending on the DEFINER value, as described later in this section. If
binary logging is enabled, CREATE TRIGGER might require the SUPER
privilege, as described in
https://mariadb.com/kb/en/binary-logging-of-stored-routines/.

The DEFINER clause determines the security context to be used when
checking access privileges at trigger activation time. See later in
this section for more information.

trigger_time is the trigger action time. It can be BEFORE or AFTER to
indicate that the trigger activates before or after each row to be
modified.

trigger_event indicates the kind of statement that activates the
trigger. The trigger_event can be one of the following:

o INSERT: The trigger is activated whenever a new row is inserted into
  the table; for example, through INSERT, LOAD DATA, and REPLACE
  statements.

o UPDATE: The trigger is activated whenever a row is modified; for
  example, through UPDATE statements.

o DELETE: The trigger is activated whenever a row is deleted from the
  table; for example, through DELETE and REPLACE statements. However,
  DROP TABLE and TRUNCATE TABLE statements on the table do not activate
  this trigger, because they do not use DELETE. Dropping a partition
  does not activate DELETE triggers, either. See [HELP TRUNCATE TABLE].

URL: https://mariadb.com/kb/en/create-trigger/

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> 

MariaDB [yinzhengjie]> HELP CREATE TRIGGER

Syntax:
CREATE
    [DEFINER = { user | CURRENT_USER }]
    TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW trigger_body

说明：
trigger_name：
　　触发器的名称
trigger_time：
　　{ BEFORE | AFTER }，表示在事件之前或之后触发
trigger_event：
　　{ INSERT |UPDATE | DELETE }，触发的具体事件
tbl_name：
　　该触发器作用在表名

二.触发器案例展示

1>.创建测试表

MariaDB [yinzhengjie]> CREATE TABLE student_info (
    ->     stu_id INT(11) NOT NULL AUTO_INCREMENT,
    ->     stu_name VARCHAR(255) DEFAULT NULL,
    ->     PRIMARY KEY (stu_id)
    -> );
Query OK, 0 rows affected (0.01 sec)

MariaDB [yinzhengjie]> CREATE TABLE student_count (
    ->     student_count INT(11) DEFAULT 0
    -> );
Query OK, 0 rows affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> INSERT INTO student_count VALUES(0);
Query OK, 1 row affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_info;
Empty set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]> 

2>.创建触发器，在向学生表INSERT数据时，学生数增加，DELETE学生时，学生数减少

MariaDB [yinzhengjie]> CREATE TRIGGER trigger_student_count_insert
    -> AFTER INSERT
    -> ON student_info FOR EACH ROW
    -> UPDATE student_count SET student_count=student_count+1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> CREATE TRIGGER trigger_student_count_delete
    -> AFTER DELETE
    -> ON student_info FOR EACH ROW
    -> UPDATE student_count SET student_count=student_count-1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> 

3>.查看触发器

MariaDB [yinzhengjie]> SHOW TRIGGERS\G
*************************** 1. row ***************************
             Trigger: trigger_student_count_insert
               Event: INSERT
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count+1
              Timing: AFTER
             Created: 2019-10-28 22:20:07.74
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
*************************** 2. row ***************************
             Trigger: trigger_student_count_delete
               Event: DELETE
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count-1
              Timing: AFTER
             Created: 2019-10-28 22:20:12.02
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
2 rows in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> 

MariaDB [yinzhengjie]> SHOW TRIGGERS\G

MariaDB [yinzhengjie]> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| yinzhengjie        |
+--------------------+
4 rows in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> USE information_schema;
Database changed
MariaDB [information_schema]>
MariaDB [information_schema]> SELECT * FROM triggers WHERE trigger_name='trigger_student_count_insert'\G
*************************** 1. row ***************************
           TRIGGER_CATALOG: def
            TRIGGER_SCHEMA: yinzhengjie
              TRIGGER_NAME: trigger_student_count_insert
        EVENT_MANIPULATION: INSERT
      EVENT_OBJECT_CATALOG: def
       EVENT_OBJECT_SCHEMA: yinzhengjie
        EVENT_OBJECT_TABLE: student_info
              ACTION_ORDER: 1
          ACTION_CONDITION: NULL
          ACTION_STATEMENT: UPDATE student_count SET student_count=student_count+1
        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: 2019-10-28 22:20:07.74
                  SQL_MODE: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
                   DEFINER: root@localhost
      CHARACTER_SET_CLIENT: utf8mb4
      COLLATION_CONNECTION: utf8mb4_general_ci
        DATABASE_COLLATION: utf8_general_ci
1 row in set (0.01 sec)

MariaDB [information_schema]>
MariaDB [information_schema]> 

查询系统表information_schema.triggers的方式指定查询条件，查看指定的触发器信息。

4>.测试触发器是否执行

MariaDB [(none)]> use yinzhengjie
Database changed
MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_info;
Empty set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> INSERT INTO student_info VALUES (1,'Jason Yin'),(2,'YinZhengJie'),(3,'Shell'),(4,'Python'),(5,'Java'),(6,'Golang');
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_info;
+--------+-------------+
| stu_id | stu_name    |
+--------+-------------+
|      1 | Jason Yin   |
|      2 | YinZhengJie |
|      3 | Shell       |
|      4 | Python      |
|      5 | Java        |
|      6 | Golang      |
+--------+-------------+
6 rows in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             6 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> DELETE FROM student_info WHERE stu_id > 3;
Query OK, 3 rows affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             3 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>

MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             3 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_info;
+--------+-------------+
| stu_id | stu_name    |
+--------+-------------+
|      1 | Jason Yin   |
|      2 | YinZhengJie |
|      3 | Shell       |
+--------+-------------+
3 rows in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> TRUNCATE TABLE student_info;　　　　　　#使用TRUNCATE清空表中的数据库不会触发触发器哟，因为触发器定义时只针对了DELETE命令进行触发操作
Query OK, 0 rows affected (0.01 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_info;
Empty set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM student_count;
+---------------+
| student_count |
+---------------+
|             3 |
+---------------+
1 row in set (0.00 sec)

MariaDB [yinzhengjie]> 

MariaDB [yinzhengjie]> TRUNCATE TABLE student_info;　　　　　　　　#使用TRUNCATE清空表中的数据库不会触发触发器哟，因为触发器定义时只针对了DELETE命令进行触发操作

5>.删除触发器

MariaDB [yinzhengjie]> SHOW TRIGGERS\G
*************************** 1. row ***************************
             Trigger: trigger_student_count_insert
               Event: INSERT
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count+1
              Timing: AFTER
             Created: 2019-10-28 22:20:07.74
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
*************************** 2. row ***************************
             Trigger: trigger_student_count_delete
               Event: DELETE
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count-1
              Timing: AFTER
             Created: 2019-10-28 22:20:12.02
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
2 rows in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> DROP TRIGGER trigger_student_count_insert;
Query OK, 0 rows affected (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SHOW TRIGGERS\G
*************************** 1. row ***************************
             Trigger: trigger_student_count_delete
               Event: DELETE
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count-1
              Timing: AFTER
             Created: 2019-10-28 22:20:12.02
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> 

MariaDB [yinzhengjie]> DROP TRIGGER trigger_student_count_insert;

MariaDB [yinzhengjie]> SHOW TRIGGERS\G
*************************** 1. row ***************************
             Trigger: trigger_student_count_delete
               Event: DELETE
               Table: student_info
           Statement: UPDATE student_count SET student_count=student_count-1
              Timing: AFTER
             Created: 2019-10-28 22:20:12.02
            sql_mode: STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@localhost
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8_general_ci
1 row in set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> DROP TABLE student_count;
Query OK, 0 rows affected (0.01 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> DROP TABLE student_info;　　　　　　#当删除表时触发器也会随着自动删除，因为触发器是基于表的，当表都不存在了触发器也没有意义了。
Query OK, 0 rows affected (0.01 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SHOW TRIGGERS\G
Empty set (0.00 sec)

MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> 

MariaDB [yinzhengjie]> DROP TABLE student_info;　　　　　　#当删除表时触发器也会随着自动删除，因为触发器是基于表的，当表都不存在了触发器也没有意义了。