有一个表user,字段分别有id、nick_name、password、email、phone。
一、单字段(nick_name)
查出所有有重复记录的所有记录
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select * from user where nick_name in ( select nick_name from user group by nick_name having count (nick_name)>1);
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查出有重复记录的各个记录组中id最大的记录
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select * from user where id in ( select max (id) from user group by nick_name having count (nick_name)>1);
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查出多余的记录,不查出id最小的记录
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select * from user where nick_name in ( select nick_name from user group by nick_name having count (nick_name)>1) and id not in ( select min (id) from user group by nick_name having count (nick_name)>1);
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删除多余的重复记录,只保留id最小的记录
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delete from user where nick_name in ( select nick_name from ( select nick_name from user group by nick_name having count (nick_name)>1) as tmp1) and id not in ( select id from ( select min (id) from user group by nick_name having count (nick_name)>1) as tmp2);
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二、多字段(nick_name,password)
查出所有有重复记录的记录
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select * from user where (nick_name, password ) in ( select nick_name, password from user group by nick_name, password where having count (nick_name)>1);
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查出有重复记录的各个记录组中id最大的记录
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select * from user where id in ( select max (id) from user group by nick_name, password where having count (nick_name)>1);
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查出各个重复记录组中多余的记录数据,不查出id最小的一条
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select * from user where (nick_name, password ) in ( select nick_name, password from user group by nick_name, password having count (nick_name)>1) and id not in ( select min (id) from user group by nick_name, password having count (nick_name)>1);
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删除多余的重复记录,只保留id最小的记录
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delete from user where (nick_name, password ) in ( select nick_name, password from ( select nick_name, password from user group by nick_name, password having count (nick_name)>1) as tmp1) and id not in ( select id from ( select min (id) id from user group by nick_name, password having count (nick_name)>1) as tmp2);
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原文链接:https://www.addcoder.com/blog/article_detail/edbhoezw/