mysql触发器实时检测一条语句进行备份删除思路详解

问题描述：用户有一个这样一个需求，在一张表里会不时出现 “违规” 字样的字段，需要在出现这个字段的时候，把整行的数据删掉。这是个采集任务，如果发现有“违规”字样的数据，会整点或者什么时间进行统一上报，也无法对源头进行控制让这种数据不生成。

现在需要实现以下需求：

1.实时检测这条数据的产生，发现后删除

2.在删除之前作备份这条数据

解决思路：

需要明确解决思路，

1.首先是如何实时探测删除？询问开发，这条数据的生成方式为insert，就可以做一个当表做插入的时候，然后做一个after insert 做delete数据的触发器

2.如何进行备份？何种方式备份？能不能备份到一个表里，这个表里记录每次插入的时间，建立这个备份表可以取与原表结构基本相同，但是备份表要删除原表的自增属性，主键，外键等属性，新增一个时间戳字段，方便记录每次备份数据的时间，删除以上属性是为了能够把数据写入备份表中

3.如何在删除之前做备份呢？一开始想的是放到一个触发器就行，先把数据进行备份，然后后面跟着一条删除，测试的时候行不通

测试方案：

先准备一些测试数据和测试表

1.建立测试数据

mysql> show create table student;
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table   | create table                                                                                                                                                                                                                                                             |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | create table `student` (
  `sno` char(9) not null,
  `sname` char(20) not null,
  `ssex` char(2) default null,
  `sage` smallint default null,
  `sdept` char(20) default null,
  primary key (`sno`)
) engine=innodb default charset=utf8mb4 collate=utf8mb4_0900_ai_ci |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

2.建立备份表。查看建表语句，正式环境是不知道原表的表结构的，需要有改原表结构，并创建新备份表的操作的

原表建表语句

mysql> show create table student;
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table   | create table                                                                                                                                                                                                                                                             |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | create table `student` (
  `sno` char(9) not null,
  `sname` char(20) not null,
  `ssex` char(2) default null,
  `sage` smallint default null,
  `sdept` char(20) default null,
  primary key (`sno`)
) engine=innodb default charset=utf8mb4 collate=utf8mb4_0900_ai_ci |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

3.准备备份语句，删除语句，插入测试语句

备份语句（因为备份表多一个时间戳的字段，所以备份语句要做修改一下）

mysql> show create table student_bak;
+-------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| table | create table |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student_bak | create table `student_bak` (
`sno` char(9) not null,
`sname` char(20) not null,
`ssex` char(2) default null,
`sage` smallint default null,
`sdept` char(20) default null,
`create_date` timestamp not null default current_timestamp
) engine=innodb default charset=utf8mb4 collate=utf8mb4_0900_ai_ci |
+-------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

备份效果

插入测试语句：

insert into student values('201215124','张三','男',20,'el');

删除语句（删除数据一定要写精准了，到时候删什么，就要备份什么）

delete from student where sdept='el';

4.实际测试方案

4.1 把两条语句写进一个触发器(操作失败，逻辑执行不成功)

drop trigger if exists test_trigger;
delimiter $
create trigger test_trigger
after
insert on student2
for each row
begin
insert into student_bak(sno,sname,ssex,sage,sdept) select * from student where sdept='el';
delete from student where sdept='el';
end $
delimiter ;

4.2 准备两个单独的触发器，一个是当原表出现这条数据时，插入到备份表实现备份的效果。第二个触发器是做备份表备份完数据之后，在做一个删除原表该条数据的触发器，然后实现备份完删除的效果（还是操作失败），执行报错，说的是触发器有冲突还是什么的，这样做让数据库不知道执行逻辑了。

4.3 做一个在原表如果进行删除目标数据，然后备份该条数据到备份表的触发器。最后再实现实时探测目标数据出现然后删除的操作就行了，不局限于触发器的思维，做一个定时任务就可以了（操作成功）

比如下面测试的当数据库的表中sdept字段出现了一个叫‘el'的字段时，需要把整行数据删除掉

drop trigger if exists student_bak_trigger;
delimiter $
create trigger student_bak_trigger 
before 
delete on student 
for each row 
begin   
insert into  student_bak(sno,sname,ssex,sage,sdept) select * from student where sdept='el';
end $
delimiter ;

这个触发器就实现了，如果原表的目标数据被删除了，触发器触发了就会备份该条数据

mysql> select * from student;
+-----------+--------+------+------+-------+
| sno       | sname  | ssex | sage | sdept |
+-----------+--------+------+------+-------+
| 201215121 | 李勇   | 男   |   20 | cs    |
| 201215122 | 刘晨   | 女   |   19 | cs    |
| 201215123 | 王敏   | 女   |   18 | ma    |
| 201215130 | 兵丁   | 男   |   20 | ch    |
+-----------+--------+------+------+-------+
4 rows in set (0.00 sec)

mysql> select * from student_bak;
+-----------+--------+------+------+-------+---------------------+
| sno       | sname  | ssex | sage | sdept | create_date         |
+-----------+--------+------+------+-------+---------------------+
| 201215124 | 张三   | 男   |   20 | el    | 2021-09-18 15:42:20 |
+-----------+--------+------+------+-------+---------------------+
1 row in set (0.00 sec)

mysql> insert into student values('201215125','王五','男',30,'el');
query ok, 1 row affected (0.00 sec)

mysql> select * from student;
+-----------+--------+------+------+-------+
| sno       | sname  | ssex | sage | sdept |
+-----------+--------+------+------+-------+
| 201215121 | 李勇   | 男   |   20 | cs    |
| 201215122 | 刘晨   | 女   |   19 | cs    |
| 201215123 | 王敏   | 女   |   18 | ma    |
| 201215125 | 王五   | 男   |   30 | el    |
| 201215130 | 兵丁   | 男   |   20 | ch    |
+-----------+--------+------+------+-------+
5 rows in set (0.00 sec)

mysql> select * from student_bak;
+-----------+--------+------+------+-------+---------------------+
| sno       | sname  | ssex | sage | sdept | create_date         |
+-----------+--------+------+------+-------+---------------------+
| 201215124 | 张三   | 男   |   20 | el    | 2021-09-18 15:42:20 |
+-----------+--------+------+------+-------+---------------------+
1 row in set (0.00 sec)

mysql> delete from student where sdept='el';
query ok, 1 row affected (0.01 sec)

mysql> select * from student_bak;
+-----------+--------+------+------+-------+---------------------+
| sno       | sname  | ssex | sage | sdept | create_date         |
+-----------+--------+------+------+-------+---------------------+
| 201215124 | 张三   | 男   |   20 | el    | 2021-09-18 15:42:20 |
| 201215125 | 王五   | 男   |   30 | el    | 2021-09-18 15:47:28 |
+-----------+--------+------+------+-------+---------------------+
2 rows in set (0.00 sec)

最后实现一个定时任务，来循环的删除一个叫‘el'的字段的整行数据，这里的定时任务是面向全局的，一定要加上数据库名和具体表名，定时任务的执行速度是可以手动调整的，下面为3s/次,以便实现需要的效果

create event if not exists e_test_event
on schedule every 3 second 
on completion preserve
do delete from abc.student where sdept='el'; 

关闭定时任务：

mysql> alter event e_test_event on completion preserve disable;
query ok, 0 rows affected (0.00 sec)

查看定时任务：

mysql> select * from information_schema.events\g;*************************** 4. row ***************************
       event_catalog: def
        event_schema: abc
          event_name: e_test_event
             definer: root@%
           time_zone: system
          event_body: sql
    event_definition: delete from abc.student where sdept='el'
          event_type: recurring
          execute_at: null
      interval_value: 3
      interval_field: second
            sql_mode: only_full_group_by,strict_trans_tables,no_zero_in_date,no_zero_date,error_for_division_by_zero,no_engine_substitution
              starts: 2021-09-17 13:35:44
                ends: null
              status: enabled
       on_completion: preserve
             created: 2021-09-17 13:35:44
        last_altered: 2021-09-17 13:35:44
       last_executed: 2021-09-18 15:43:35
       event_comment: 
          originator: 3330614
character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
  database_collation: utf8mb4_0900_ai_ci
4 rows in set (0.00 sec)

查看触发器：

mysql> select * from information_schema.triggers\g;
*************************** 5. row ***************************
           trigger_catalog: def
            trigger_schema: abc
              trigger_name: student_bak_trigger
        event_manipulation: delete
      event_object_catalog: def
       event_object_schema: abc
        event_object_table: student
              action_order: 1
          action_condition: null
          action_statement: begin   
insert into  student_bak(sno,sname,ssex,sage,sdept) select * from student where sdept='el';
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: 2021-09-18 15:41:48.53
                  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@%
      character_set_client: utf8mb4
      collation_connection: utf8mb4_0900_ai_ci
        database_collation: utf8mb4_0900_ai_ci
5 rows in set (0.00 sec)

实现效果：

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