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数据库中抽取n条随机记录

随机取出n条记录:
Sql server:select top n * from 表 order by newid()
Access:Select top n * FROM 表 orDER BY Rnd(id)
mysql:Select * From 表 order By rand() Limit n
select * from youtab where mod ( rowid , 3 ) = 0
建议把MSSQL的联机丛书中的 Transact-SQL 参考大致看一遍,很多东西就心中有数了

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select * from tablename order by rand() limit 10
mysql中随机提取数据库记录
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select top 10 * from tablename order by NEWID()
sqlserver中随机提取数据库记录

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SELECT top 10 * FROM tablename ORDER BY Rnd(FId)
FId:为你当前表的ID字段名

Access中随机提取数据库记录

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删除数据库重复记录并且只保留一条记录

在n条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复并保留一条呢?方法如下:

 

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 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)

 

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)

 

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)