sql语句去除重复记录（多表连接的查询）--处理表重复记录(查询和删除)
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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
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--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)
--> --> ⽣成測試數據
if not object_id('Tempdb..#T') is null
drop table#T
Go
Create table#T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert#T
select1,N'A',N'A1'union all
select2,N'A',N'A2'union all
select3,N'A',N'A3'union all
select4,N'B',N'B1'union all
select5,N'B',N'B2'
Go
--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#T a where not exists(select1 from#T where Name=a.Name and ID<a.ID)
⽅法2:
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3:
select* from#T a where ID=(select min(ID) from#T where Name=a.Name)
⽅法4:
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5:
select* from#T a group by ID,Name,Memo having ID=(select min(ID)from#T where Name=a.Name)
⽅法6:
select* from#T a where(select count(1) from#T where Name=a.Name and ID<a.ID)=0
⽅法7:
select* from#T a where ID=(select top1 ID from#T where Name=a.name order by ID)
⽅法8:
select* from#T a where ID!>all(select ID from#T where Name=a.Name)
⽅法9(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10:
select ID,Name,Memo from(select*,min(ID)over(partition by Name) as MinID from#T 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#T 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#T a where not exists(select1 from#T where Name=a.Name and ID>a.ID)
⽅法2:
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3:
select* from#T a where ID=(select max(ID) from#T where Name=a.Name) order by ID
⽅法4:
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5:
select* from#T a group by ID,Name,Memo having ID=(select max(ID)from#T where Name=a.Name)
⽅法6:
select* from#T a where(select count(1) from#T where Name=a.Name and ID>a.ID)=0
⽅法7:
select* from#T a where ID=(select top1 ID from#T where Name=a.name order by ID desc)
⽅法8:
select* from#T a where ID!<all(select ID from#T where Name=a.Name)
⽅法9(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10:
select ID,Name,Memo from(select*,max(ID)over(partition by Name) as MinID from#T 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#T 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
--> --> ⽣成測試數據
if not object_id('Tempdb..#T') is null
drop table#T
Go
Create table#T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))
Insert#T
select1,N'A',N'A1'union all
select2,N'A',N'A2'union all
select3,N'A',N'A3'union all
select4,N'B',N'B1'union all
select5,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#T a where exists(select1 from#T where Name=a.Name and ID<a.ID)
⽅法2:
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3:
delete a from#T a where ID not in(select min(ID) from#T where Name=a.Name)
⽅法4(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5:
delete a from#T a where(select count(1) from#T where Name=a.Name and ID<a.ID)>0
⽅法6:
delete a from#T a where ID<>(select top1 ID from#T where Name=a.name order by ID)
⽅法7:
delete a from#T a where ID>any(select ID from#T where Name=a.Name)
select* from#T
⽣成结果:
/*
ID          Name Memo
----------- ---- ----
1          A    A1
4          B    B1
(2 ⾏受影响)
*/
--II、Name相同ID保留最⼤的⼀条记录:
⽅法1:
delete a from#T a where exists(select1 from#T where Name=a.Name and ID>a.ID)
⽅法2:
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3:
delete a from#T a where ID not in(select max(ID) from#T where Name=a.Name)
⽅法4(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5:
delete a from#T a where(select count(1) from#T where Name=a.Name and ID>a.ID)>0
⽅法6:
delete a from#T a where ID<>(select top1 ID from#T where Name=a.name order by ID desc)
⽅法7:
delete a from#T a where ID<any(select ID from#T where Name=a.Name)
select* from#T
/*
ID          Name Memo
----------- ---- ----
3          A    A3
5          B    B2
(2 ⾏受影响)
*/
--3、删除重复记录没有⼤⼩关系时，处理重复值
--> --> ⽣成測試數據
if not object_id('Tempdb..#T') is null
drop table#T
Go
Create table#T([Num] int,[Name] nvarchar(1))
Insert#T
select1,N'A'union all
select1,N'A'union all
select1,N'A'union all
select2,N'B'union all
select2,N'B'
Go
⽅法1:
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
/*
Num        Name
----------- ----
1          A
2          B
sql中union多表合并(2 ⾏受影响)
*/
--重新执⾏测试数据后⽤⽅法2
⽅法2:
alter table#T add ID int identity--新增标识列
go
delete a from#T a where exists(select1 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
/*
Num        Name
----------- ----
1          A
2          B
(2 ⾏受影响)
*/
--重新执⾏测试数据后⽤⽅法3
⽅法3:
declare Roy_Cursor cursor local for
select count(1)-1,Num,Name from#T group by Num,Name having count(1)>1
declare@con int,@Num int,@Name nvarchar(1)
open Roy_Cursor
fetch next from Roy_Cursor into@con,@Num,@Name
while @@Fetch_status=0
begin
set rowcount @con;
delete#T where Num=@Num and Name=@Name
set rowcount 0;
fetch next from Roy_Cursor into@con,@Num,@Name
end
close Roy_Cursor
deallocate Roy_Cursor
--查看结果
select* from#T /*
Num        Name ----------- ----
1          A
2          B
(2 ⾏受影响)
*/

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