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
create table Student(Sno char(9) primary key,Sname char(20) not null,Ssex char(2),Sage smallint,Sdept char(20));
create table Course(Cno char(4) primary key,Cname char(40) not null,Cpno char(4) references Course(Cno),Ccredit smallint);
create table SC(Sno char(9),Cno char(4),Grade smallint,primary key(Sno,Cno),foreign key(Sno) references Student(Sno),foreign key (Cno) references Course(Cno));
insert into Student(Sno,Sname,Ssex,Sage,Sdept)values('201215121','李勇','男','20','CS');
insert into Student(Sno,Sname,Ssex,Sage,Sdept)values('201215122','刘晨','女','19','CS');
insert into Student(Sno,Sname,Ssex,Sage,Sdept)values('201215123','王敏','女','18','MA');
insert into Course(Cno,Cname,Cpno,Ccredit)values('1','数据库','5','4');
insert into Course(Cno,Cname,Cpno,Ccredit)values('2','数学','null','2');
insert into Course(Cno,Cname,Cpno,Ccredit)values('3','信息系统','1','4');
insert into Course(Cno,Cname,Cpno,Ccredit)values('4','操作系统','6','3');
insert into Course(Cno,Cname,Cpno,Ccredit)values('5','数据结构','7','4');
insert into Course(Cno,Cname,Cpno,Ccredit)values('6','数据处理','null','2');
insert into Course(Cno,Cname,Cpno,Ccredit)values('7','PASCLA语言','6','4');
insert into SC(Sno,Cno,Grade)values('201215121','1','92');
insert into SC(Sno,Cno,Grade)values('201215121','2','85');
insert into SC(Sno,Cno,Grade)values('201215121','3','88');
insert into SC(Sno,Cno,Grade)values('201215122','2','90');
insert into SC(Sno,Cno,Grade)values('201215122','3','80');
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)
修改后的备份表
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)
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）
insert into student_bak(Sno,Sname,Ssex,Sage,Sdept) select * from student where Sdept='MA';
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.eventsG;
*************************** 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.triggersG; *************************** 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：
