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*FROMblog_user_relationaWHERE(a.account_instance_id,a.follow_account_instance_id) IN(SELECTaccount_instance_id,follow_account_instance_idFROMblog_user_relationGROUPBYaccount_instance_id,follow_account_instance_idHAVING 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*/ CREATETABLEblog_user_relation_tempAS ( SELECT*FROMblog_user_relationaWHERE (a.account_instance_id,a.follow_account_instance_id) IN(SELECTaccount_instance_id,follow_account_instance_idFROMblog_user_relationGROUPBYaccount_instance_id,follow_account_instance_idHAVINGCOUNT(*)>1) AND relation_id NOTIN(SELECTMIN(relation_id)FROMblog_user_relationGROUPBYaccount_instance_id,follow_account_instance_idHAVINGCOUNT(*)>1)); /*删除数据*/ DELETEFROM`blog_user_relation`WHERErelation_idIN(SELECTrelation_idFROMblog_user_relation_temp); /*删除临时表*/ DROPTABLEblog_user_relation_temp;