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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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  • 原文地址:https://www.cnblogs.com/lovesong/p/3834195.html
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