SQL删除重复数据只保留一条

最新推荐文章于 2023-11-22 09:40:11 发布

转载最新推荐文章于 2023-11-22 09:40:11 发布 · 317 阅读

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原文链接：https://blog.youkuaiyun.com/anya/article/details/6407280

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这篇博客分享了如何使用SQL语句来查找并删除数据库表中的重复记录。提供了针对单个字段和多个字段重复情况的删除方法，并解决了在执行删除操作时可能遇到的错误。还提到了更新字段特定部分的技巧以及模拟删除（设置标志为无效）不包含最小ROWID的重复记录。

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https://blog.youkuaiyun.com/anya/article/details/6407280

在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢
1、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)

2、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 peopleName in (select peopleName from people group by peopleName having count(peopleName) > 1)
and peopleId not in (select min(peopleId) from people group by peopleName having count(peopleName)>1)

3、查找表中多余的重复记录（多个字段）
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、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)

注：如果遇到报错：

delete from student where name in ( select name from student group by name having count(name)>1 ) and age in ( select min(age) from student group by name having count(name)>1 ) ;
ERROR 1093 (HY000): Table 'student' is specified twice, both as a target for 'DELETE' and as a separate source for data

则使用别名：

delete from student where name in ( select * from (select name from student group by name having count(name)>1 ) as t1 ) and age in ( select * from (select min(age) from student group by name having count(name)>1 ) as t2 ) ;
Query OK, 1 row affected (0.01 sec)

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录
select * 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)

6.消除一个字段的左边的第一位：

update tableName set [Title]=Right([Title],(len([Title])-1)) where Title like '村%'

7.消除一个字段的右边的第一位：

update tableName set [Title]=left([Title],(len([Title])-1)) where Title like '%村'

8.假删除表中多余的重复记录（多个字段），不包含rowid最小的记录
update vitae set ispass=-1
where peopleId in (select peopleId from vitae group by peopleId