本文摘自PHP中文网,作者醉折花枝作酒筹,侵删。
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
1 2 | 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
1 2 3 | 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)
1 2 | 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
1 2 3 | 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
1 2 3 | 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:
1 | 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:
1 | 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
1 | update vitae set ispass=-1where peopleId in (select peopleId from vitae group by peopleId
|
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