Mysql一些复杂的sql语句(查询与删除重复的行)

1.查找重复的行

				?

									SELECT * FROM blog_user_relation a WHERE (a.account_instance_id,a.follow_account_instance_id) 

									IN (SELECT account_instance_id,follow_account_instance_id FROM blog_user_relation GROUP BY account_instance_id, follow_account_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.account_instance_id,a.follow_account_instance_id) 

									 IN ( SELECT account_instance_id,follow_account_instance_id FROM blog_user_relation GROUP BY account_instance_id, follow_account_instance_id HAVING COUNT(*) > 1)

									 AND

									 relation_id 

									 NOT IN (SELECT MIN(relation_id) FROM blog_user_relation GROUP BY account_instance_id, follow_account_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;

Mysql一些复杂的sql语句(查询与删除重复的行)

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