SQL如何删除重复数据

在sql中，可以使用select语句删除重复数据，语法为：“select * from 字段 where 字段id in (select 字段id from 字段 group by 字段 having count(字段id) > 1)”。

本教程操作环境：windows7系统、mysql8.0版本、Dell G3电脑。

用SQL语句,删除掉重复项只保留一条

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

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)

扩展：

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)

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)

 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)

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)

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%'

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'

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=-1where peopleId in (select peopleId from vitae group by peopleId

相关推荐：《mysql教程》

Atas ialah kandungan terperinci SQL如何删除重复数据. Untuk maklumat lanjut, sila ikut artikel berkaitan lain di laman web China PHP!