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  • MySQL 删除数据库中重复数据方法

    1. 查询需要删除的记录,会保留一条记录。

    select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id< b.bid where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid
    

     2. 删除重复记录,只保留一条记录。注意,subject,RECEIVER 要索引,否则会很慢的。

    delete a from test1 a, (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b where a.subject=b.subject and a.RECEIVER = b.RECEIVER and a.id < b.bid;
    

     3. 查找表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断

    select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
    

     4. 删除表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断,只留有rowid最小的记录

    delete from people where peopleId in (select peopleId from people group by peopleId  having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
    

     5.删除表中多余的重复记录(多个字段),只留有rowid最小的记录

    delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
    

     http://www.jb51.net/article/23964.htm

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  • 原文地址:https://www.cnblogs.com/zhuiluoyu/p/7607921.html
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