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Mysql一些复杂的语句
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;
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