sql关于查询不重复记录的操作可是老问题了，经常查，所就在这里总整理一下，大家分享一下~

假设表存在ID，Name列，Num列，ID为自增列

sql关于查询不重复记录的操作可是老问题了，经常查，所就在这里总整理一下，大家分享一下~

假设表存在ID，Name列，Num列，ID为自增列

1、Num、Name相同的重复值记录,没有大小关系只保留一条
2、Name相同,ID有大小关系时,保留大或小其中一个记录

--1、用于查询重复处理记录(如果列没有大小关系时2000用生成自增列和临时表处理,SQL2005用row_number函数处理

--I、Name相同ID最小的记录(推荐用1,2,3),方法3在SQl05时，效率高于1、2
方法1:
Select * from 表 as as a where not exists(select 1 from 表 where Name=a.Name and ID<a.ID)

方法2:
select a.* from 表 as a join (select min(ID)ID,Name from 表 group by Name) b on a.Name=b.Name and a.ID=b.ID

方法3:
select * from 表 as a where ID=(select min(ID) from 表 where Name=a.Name)

方法4:
select a.* from 表 as a join 表 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5:
select * from 表 as a group by ID,Name,Memo having ID=(select min(ID)from 表 where Name=a.Name)

方法6:
select * from 表 as a where (select count(1) from 表 where Name=a.Name and ID<a.ID)=0

方法7:
select * from 表 as a where ID=(select top 1 ID from 表 where Name=a.name order by ID)

方法8:
select * from 表 as a where ID!>all(select ID from 表 where Name=a.Name)

方法9(注:ID为唯一时可用):
select * from 表 as a where ID in(select min(ID) from 表 group by Name)

--SQL2005:

方法10:
select ID,Name,Memo from (select *,min(ID)over(partition by Name) as MinID from 表 as a)T where ID=MinID

方法11:

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

生成结果:
/*
ID          Name Memo
----------- ---- ----
1           A    A1
4           B    B1

(2 行受影响)
*/

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

方法2:
select a.* from 表 as a join (select max(ID)ID,Name from 表 group by Name) b on a.Name=b.Name and a.ID=b.ID order by ID

方法3:
select * from 表 as a where ID=(select max(ID) from 表 where Name=a.Name) order by ID

方法4:
select a.* from 表 as a join 表 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5:
select * from 表 as a group by ID,Name,Memo having ID=(select max(ID)from 表 where Name=a.Name)

方法6:
select * from 表 as a where (select count(1) from 表 where Name=a.Name and ID>a.ID)=0

方法7:
select * from 表 as a where ID=(select top 1 ID from 表 where Name=a.name order by ID desc)

方法8:
select * from 表 as a where ID!<all(select ID from 表 where Name=a.Name)

方法9(注:ID为唯一时可用):
select * from 表 as a where ID in(select max(ID) from 表 group by Name)

--SQL2005:

方法10:
select ID,Name,Memo from (select *,max(ID)over(partition by Name) as MinID from 表 as a)T where ID=MinID

方法11:
select ID,Name,Memo from (select *,row_number()over(partition by Name order by ID desc) as MinID from 表 as a)T where MinID=1

生成结果2:
/*
ID          Name Memo
----------- ---- ----
3           A    A3
5           B    B2

(2 行受影响)
*/

--2、删除重复记录有大小关系时,保留大或小其中一个记录

--> --> (Roy)生成測試數據

if not object_id('Tempdb..表') is null
    drop table 表
Go
Create table 表([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert 表
select 1,N'A',N'A1' union all
select 2,N'A',N'A2' union all
select 3,N'A',N'A3' union all
select 4,N'B',N'B1' union all
select 5,N'B',N'B2'
Go

--I、Name相同ID最小的记录(推荐用1,2,3),保留最小一条
方法1:
delete a from 表 as a where exists(select 1 from 表 where Name=a.Name and ID<a.ID)

方法2:
delete a from 表 as a left join (select min(ID)ID,Name from 表 group by Name) b on a.Name=b.Name and a.ID=b.ID where b.Id is null

方法3:
delete a from 表 as a where ID not in (select min(ID) from 表 where Name=a.Name)

方法4(注:ID为唯一时可用):
delete a from 表 as a where ID not in(select min(ID)from 表 group by Name)

方法5:
delete a from 表 as a where (select count(1) from 表 where Name=a.Name and ID<a.ID)>0

方法6:
delete a from 表 as a where ID<>(select top 1 ID from 表 where Name=a.name order by ID)

方法7:
delete a from 表 as a where ID>any(select ID from 表 where Name=a.Name)

select * from 表

生成结果:
/*
ID          Name Memo
----------- ---- ----
1           A    A1
4           B    B1

(2 行受影响)
*/