使用SQL命令的in&not in等删除数据的总结

总结：
1、查询时用 not in 效率极其低下，因此结合left join改为in查询，效率很快

原语句:

 select * from my_test_table where id not in (select b.id as id from ( SELECT MAX(a.`ModifyAt`)ModifyAt,a.userid FROM my_test_table a   GROUP BY a.UserId,a.SeriesId,a.CourseId) c
 INNER JOIN `my_test_table` b ON c.userid=b.userid AND c.ModifyAt=b.ModifyAt)

优化后：

select * from (select u.id as id from my_test_table u left join  (select b.id as id from ( SELECT MAX(a.`ModifyAt`)ModifyAt,a.userid FROM my_test_table a   GROUP BY a.UserId,a.SeriesId,a.CourseId) c
 INNER JOIN `my_test_table` b ON c.userid=b.userid AND c.ModifyAt=b.ModifyAt) d  on d.id = u.id where d.Id is null) as e

2、查询出后，需要用 delete where in 来删除，但是delete where in 语句效率极其低下。

原语句：

delete from my_test_table where id in (select * from (select u.id as id from my_test_table u left join  (select b.id as id from ( SELECT MAX(a.`ModifyAt`)ModifyAt,a.userid FROM my_test_table a   GROUP BY a.UserId,a.SeriesId,a.CourseId) c
 INNER JOIN `my_test_table` b ON c.userid=b.userid AND c.ModifyAt=b.ModifyAt) d  on d.id = u.id where d.Id is null) as e)

因此改为where语句，关联表删除数据 优化后：

delete deluser from my_test_table deluser,(select * from (select u.id as id from my_test_table u left join  (select b.id as id from ( SELECT MAX(a.`ModifyAt`)ModifyAt,a.userid FROM my_test_table a   GROUP BY a.UserId,a.SeriesId,a.CourseId) c
 INNER JOIN `my_test_table` b ON c.userid=b.userid AND c.ModifyAt=b.ModifyAt) d  on d.id = u.id where d.Id is null) as e) f where deluser.id = f.id;

0.36秒执行完成。

参考文章：

https://blog.csdn.net/hello_l/article/details/71419464

https://blog.csdn.net/pcwblover008/article/details/80015855