《Mysql必讀Mysql一些復雜的sql語句(查詢與刪除重復的行)》要點：
本文介紹了Mysql必讀Mysql一些復雜的sql語句(查詢與刪除重復的行)，希望對您有用。如果有疑問，可以聯系我們。
MYSQL教程1.查找重復的行
MYSQL教程
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)
MYSQL教程2.刪除重復的行(保留一條)
MYSQL教程PS：因為mysql的delete,如果被刪的表的where條件里有in,且in里面也有此表,那就刪除不了.
MYSQL教程
/*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;
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