MySql数据查重、去重的实现
2019年5月31日一、单字段（nick_name）
1、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); |
2、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); |
3、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); |
4、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); |
二、多字段（nick_name,password）
1、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); |
2、查出有重复记录的各个记录组中id最大的记录
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1 2 |
select * from user where id in (select max(id) from user group by nick_name,password where having count(nick_name)>1); |
3、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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1 2 3 4 |
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); |
4、删除多余的重复记录，只保留id最小的记录
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1 2 3 4 5 6 |
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); |
