SQL操作语句之查询及删除重复记录的方法

--I、Name相同ID最小的记录,方法在SQl05时，效率高于、
方法:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID<a.ID)

方法:
select a.* from #T a join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID

方法:
select * from #T a where ID=(select min(ID) from #T where Name=a.Name)

方法:
select a.* from #T a join #T b on a.Name=b.Name and a.ID>=b.ID group by a.ID,a.Name,a.Memo having count(1)=1 

方法:
select * from #T a group by ID,Name,Memo having ID=(select min(ID)from #T where Name=a.Name)

方法:
select * from #T a where (select count(1) from #T where Name=a.Name and ID0

方法:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID)

方法:
select * from #T a where ID!>all(select ID from #T where Name=a.Name)

方法(注:ID为唯一时可用):
select * from #T a where ID in(select min(ID) from #T group by Name)

--SQL2005:

方法:
select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from #T a)T where ID=MinID

方法:

select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID) as MinID from #T a)T where MinID=1

--II、Name相同ID最大的记录,与min相反:
方法:
Select * from #T a where not exists(select 1 from #T where Name=a.Name and ID>a.ID)

方法:
select a.* from #T a join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID order by ID

方法:
select * from #T a where ID=(select max(ID) from #T where Name=a.Name) order by ID

方法:
select a.* from #T a join #T b on a.Name=b.Name and a.ID<=b.ID group by a.ID,a.Name,a.Memo having count(1)=1 

方法:
select * from #T a group by ID,Name,Memo having ID=(select max(ID)from #T where Name=a.Name)

方法:
select * from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)=0

方法:
select * from #T a where ID=(select top 1 ID from #T where Name=a.name order by ID desc)

方法:
select * from #T a where ID!select ID from #T where Name=a.Name)

方法(注:ID为唯一时可用):
select * from #T a where ID in(select max(ID) from #T group by Name)

--SQL2005:

方法:
select ID,Name,Memo from (select *,max(ID)over(partition by Name) as MinID from #T a)T where ID=MinID

方法:
select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID desc) as MinID from #T a)T where MinID=1

--I、Name相同ID最小的记录,保留最小一条
方法:
delete a from #T a where  exists(select 1 from #T where Name=a.Name and ID<a.ID)

方法:
delete a  from #T a left join (select min(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null

方法:
delete a from #T a where ID not in (select min(ID) from #T where Name=a.Name)

方法(注:ID为唯一时可用):
delete a from #T a where ID not in(select min(ID)from #T group by Name)

方法:
delete a from #T a where (select count(1) from #T where Name=a.Name and ID0

方法:
delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID)

方法:
delete a from #T a where ID>any(select ID from #T where Name=a.Name)

--II、Name相同ID保留最大的一条记录:

方法:
delete a from #T a where  exists(select 1 from #T where Name=a.Name and ID>a.ID)

方法:
delete a  from #T a left join (select max(ID)ID,Name from #T group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null

方法:
delete a from #T a where ID not in (select max(ID) from #T where Name=a.Name)

方法(注:ID为唯一时可用):
delete a from #T a where ID not in(select max(ID)from #T group by Name)

方法:
delete a from #T a where (select count(1) from #T where Name=a.Name and ID>a.ID)>0

方法:
delete a from #T a where ID<>(select top 1 ID from #T where Name=a.name order by ID desc)

方法:
delete a from #T a where IDselect ID from #T where Name=a.Name)

--3、删除重复记录没有大小关系时，处理重复值
方法:
if object_id('Tempdb..#') is not null
    drop table #
Select distinct * into # from #T--排除重复记录结果集生成临时表#

truncate table #T--清空表

insert #T select * from #    --把临时表#插入到表#T中

--查看结果
select * from #T



--重新执行测试数据后用方法
方法:

alter table #T add ID int identity--新增标识列
go
delete a from  #T a where  exists(select 1 from #T where Num=a.Num and Name=a.Name and ID>a.ID)--只保留一条记录
go
alter table #T drop column ID--删除标识列

--查看结果
select * from #T