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Mysql一些復雜的sql語句(查詢與刪除重復的行)

投稿：mdxy-dxy

1.查找重復的行

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.刪除重復的行(保留一條)

PS：因為mysql的delete，如果被刪的表的where條件裡有in，且in裡面也有此表，那就刪除不了。

/*創建個臨時表*/
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));

/*刪除數據*/
DELETE FROM `blog_user_relation` WHERE relation_id IN (SELECT relation_id FROM blog_user_relation_temp);

/*刪除臨時表*/
DROP TABLE blog_user_relation_temp;