Mysql一些复杂的sql语句(查询与删除重复的行)
网络编程 2021-07-05 14:36www.168986.cn编程入门
这篇文章主要介绍了Mysql一些复杂的sql语句(查询与删除重复的行),需要的朋友可以参考下
1.查找重复的行
SELECT * FROM blog_user_relation a WHERE (a.aount_instance_id,a.follow_aount_instance_id) IN (SELECT aount_instance_id,follow_aount_instance_id FROM blog_user_relation GROUP BY aount_instance_id, follow_aount_instance_id HAVING COUNT(*) > 1)
2.删除重复的行(保留一条)
PS：因为mysql的delete，如果被删的表的where条件里有in，且in里面也有此表，那就删除不了。
/*创建个临时表*/ CREATE TABLE blog_user_relation_temp AS ( SELECT * FROM blog_user_relation a WHERE (a.aount_instance_id,a.follow_aount_instance_id) IN ( SELECT aount_instance_id,follow_aount_instance_id FROM blog_user_relation GROUP BY aount_instance_id, follow_aount_instance_id HAVING COUNT(*) > 1) AND relation_id NOT IN (SELECT MIN(relation_id) FROM blog_user_relation GROUP BY aount_instance_id, follow_aount_instance_id HAVING COUNT(*)>1)); /*删除数据*/ DELETE FROM `blog_user_relation` WHERE relation_id IN (SELECT relation_id FROM blog_user_relation_temp); /*删除临时表*/ DROP TABLE blog_user_relation_temp;