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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