一、触发器

　　触发器是与表有关的数据库对象，指在insert/update/delete之前或者之后，触发并执行触发器中定义的sql语句集合，触发器的这种特性可以协助应用在数据库端确保数据的完整性，日志记录，数据校验等操作。

使用别名old和new来引用触发器中发生变化的记录内容，这与其他的数据库是相似的，现在触发器还只支持行级触发，不支持语句级触发。

二、触发器类型

• insert型触发器：new表示将要或者已经新增的数据
• update型触发器：old表示修改之前的数据，new表示将要或已经修改后的数据
• delete型触发器：old表示将要或者已经删除的数据

三、触发器语法

　　3.1 创建语法

create trigger trigger_name
before/after insert/update/delete
on tb_name for each row
begin
　　trigger_stmt;
end;

　　3.2 查看语法

show triggers;

　　3.3 删除语句

drop trigger [schema_name.] trigger_name; -- 如果没有指定schema_name，默认为当前数据库

四、插入数据触发器案例

　　4.1 需求：

　　　　通过触发器记录student表的数据插入时，将变更日志插入到日志表student_logs中；

　　4.2 创建 student_logs表

mysql> create table student_logs(
-> id int primary key auto_increment,
-> operation varchar(20) comment "操作类型,insert/update/delete",
-> operate_time datetime comment "操作时间",
-> operate_id int comment "操作的ID",
-> operate_params varchar(500) comment "操作参数"
-> )comment "student操作日志表";
Query OK, 0 rows affected (1.18 sec)

　　4.3 创建插入数据触发器

mysql>delimiter &
mysql> create trigger student_insert_trigger
-> after insert on student for each row
->begin
-> insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null, 'insert', now(), new.id, concat("插入的数据内容为：id=",new.id,"name=",new.name,"age=",new.age,"score=",new.score));
->end;
->&
Query OK, 0 rows affected (0.20 sec)

　　　　说明1：delimiter &在之前的文章中已经提到过，是将mysql中的语句终止符由“；” 改为“&”,原因是，触发器中有完整的sql语句，会包含分号，如果不改，怎无法在终端中书写完整的触发器语句

　　4.4 查看创建的触发器

mysql> delimiter ;
mysql> show triggers;
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| student_insert_trigger | INSERT | student | begin insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null, 'insert', now(), new.id, concat("插入的数据内容为：id=",new.id,"name=",new.name,"age=",new.age,"score=",new.score)); end | AFTER | 2023-08-16 00:07:46.53 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)

　　　　说明2：delimiter是将sql语句终止符由“&”在改为“；”

　　4.5 插入验证

mysql> insert into student(id,name,age,score) values(null,"李白",30,100);
Query OK, 1 row affected (0.21 sec)

mysql> select * from student_logs;
+----+-----------+---------------------+------------+-----------------------------------------------------------+
| id | operation | operate_time | operate_id | operate_params |
+----+-----------+---------------------+------------+-----------------------------------------------------------+
| 1 | insert | 2023-08-16 00:21:47 | 5 | 插入的数据内容为：id=5name=李白age=30score=100 |
+----+-----------+---------------------+------------+-----------------------------------------------------------+
1 row in set (0.00 sec)

　　　　说明3：插入数据李白的信息就已经自动的在student_logs中记录

五、修改数据触发器案例

　　5.1 创建修改数据触发器

mysql>delimiter &
mysql> create trigger student_update_trigger after update on student for each row begin insert into student_logs(id, operation, operate_time,operate_id,operate_params) values (null,'update',now(),new_id,concat( '更新前数据：id=',old.id,',name=',old.name,',age=',old.age,',score=',old.score,' | 更新后数据：id=',new.id, ',name=',new.name, ',age=',new.age, ',score=',new.score)); end; &
Query OK, 0 rows affected (1.86 sec)
mysql> delimiter ;

　　5.2 查看创建的触发器

mysql> show triggers;
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| student_insert_trigger | INSERT | student | begin insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null, 'insert', now(), new.id, concat("插入的数据内容为：id=",new.id,"name=",new.name,"age=",new.age,"score=",new.score)); end | AFTER | 2023-08-16 00:07:46.53 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
| student_update_trigger | UPDATE | student | begin insert into student_logs(id, operation, operate_time,operate_id,operate_params) values (null,'update',now(),new.id,concat( '更新前数据：id=',old.id,',name=',old.name,',age=',old.age,',score=',old.score,' | 更新后数据：id=',new.id, ',name=',new.name, ',age=',new.age, ',score=',new.score)); end | AFTER | 2023-08-16 23:38:26.36 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
2 rows in set (1.16 sec)

　　5.3 查看student表原始数据

mysql> select * from student;
+----+--------+------+-------+
| id | name | age | score |
+----+--------+------+-------+
| 1 | 张三 | 18 | 88 |
| 2 | 李四 | 21 | 83 |
| 3 | 王五 | 24 | 76 |
| 4 | 赵六 | 19 | 94 |
| 5 | 李白 | 30 | 100 |
+----+--------+------+-------+
5 rows in set (1.30 sec)

　　5.4 修改student表，验证触发器

mysql> update student set age=25 where id = 5;
Query OK, 1 row affected (0.38 sec)
Rows matched: 1 Changed: 1 Warnings: 0

　　5.5 查看修改后的student表和student_logs表，验证触发器

mysql> select * from student;
+----+--------+------+-------+
| id | name | age | score |
+----+--------+------+-------+
| 1 | 张三 | 18 | 88 |
| 2 | 李四 | 21 | 83 |
| 3 | 王五 | 24 | 76 |
| 4 | 赵六 | 19 | 94 |
| 5 | 李白 | 25 | 100 |
+----+--------+------+-------+
5 rows in set (0.00 sec)

mysql> select * from student_logs;
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
| id | operation | operate_time | operate_id | operate_params |
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
| 1 | insert | 2023-08-16 00:21:47 | 5 | 插入的数据内容为：id=5name=李白age=30score=100 |
| 2 | update | 2023-08-16 23:58:23 | 5 | 更新前数据：id=5,name=李白,age=30,score=100 | 更新后数据：id=5,name=李白,age=25,score=100 |
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

六、删除数据触发器案例

　　6.1 创建删除数据触发器

mysql>delimiter &
mysql> create trigger student_delete_trigger after delete on student for each row begin insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null,'delete',now(),old.id, concat('删除之前的数据：id=',old.id, ',name=',old.name,',age=',old.age,',score=',old.score)); end;&
Query OK, 0 rows affected (0.87 sec)

　　6.2 查看触发器

mysql> show triggers;
-> &
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
| student_insert_trigger | INSERT | student | begin insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null, 'insert', now(), new.id, concat("插入的数据内容为：id=",new.id,"name=",new.name,"age=",new.age,"score=",new.score)); end | AFTER | 2023-08-16 00:07:46.53 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
| student_update_trigger | UPDATE | student | begin insert into student_logs(id, operation, operate_time,operate_id,operate_params) values (null,'update',now(),new.id,concat( '更新前数据：id=',old.id,',name=',old.name,',age=',old.age,',score=',old.score,' | 更新后数据：id=',new.id, ',name=',new.name, ',age=',new.age, ',score=',new.score)); end | AFTER | 2023-08-16 23:57:34.20 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
| student_delete_trigger | DELETE | student | begin insert into student_logs(id,operation,operate_time,operate_id,operate_params) values (null,'delete',now(),old.id, concat('删除之前的数据：id=',old.id, ',name=',old.name,',age=',old.age,',score=',old.score)); end | AFTER | 2023-08-17 00:15:46.44 | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION | skip-grants user@skip-grants host | utf8mb4 | utf8mb4_0900_ai_ci | utf8mb4_0900_ai_ci |
+------------------------+--------+---------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-----------------------------------------------------------------------------------------------------------------------+-----------------------------------+----------------------+----------------------+--------------------+
3 rows in set (0.00 sec)

　　6.3 删除数据

mysql> delimiter ;
mysql> delete from student where id = 5;
Query OK, 1 row affected (0.70 sec)

　　6.4 查看student表和student_logs表验证触发器

mysql> select * from student;
+----+--------+------+-------+
| id | name | age | score |
+----+--------+------+-------+
| 1 | 张三 | 18 | 88 |
| 2 | 李四 | 21 | 83 |
| 3 | 王五 | 24 | 76 |
| 4 | 赵六 | 19 | 94 |
+----+--------+------+-------+
4 rows in set (0.00 sec)

mysql> select * from student_logs;
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
| id | operation | operate_time | operate_id | operate_params |
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
| 1 | insert | 2023-08-16 00:21:47 | 5 | 插入的数据内容为：id=5name=李白age=30score=100 |
| 2 | update | 2023-08-16 23:58:23 | 5 | 更新前数据：id=5,name=李白,age=30,score=100 | 更新后数据：id=5,name=李白,age=25,score=100 |
| 3 | delete | 2023-08-17 00:18:06 | 5 | 删除之前的数据：id=5,name=李白,age=25,score=100 |
+----+-----------+---------------------+------------+-----------------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)