SQL重复值,去除问题

jxydhzw 2008-11-11 10:16:10
最近做一个小工具,去除一些重复数据。突然想用一条SQL语句就能实现目的。

原理就是使用 Select Distinct  和 Left Join
首先,Select Distinct 关键字段 From TableA 取出该表关键字段的唯一值。作为一个虚似表 C
然后用C表去Left Join TableA , 当TableA的关键字段=C的关键字段

示例
TableA表中的字段以及其值如下
语句 Select * As a_Distinct From tb1 效果:

fd1,fd2,fd3
1,2,3
1,3,4
2,4,3
3,5,6
2,9,6

共有5行受到影响

语句 Select Distinct a.Fd1 As a_Distinct From tb1 效果为:

a_Distinct
1
2
3
共有3行受到影响


而执行完整的SQL语句

Select b.*
From (Select Distinct a.Fd1 As a_Distinct From tb1 a) c
Left Join tb1 b On c.a_Distinct = b.Fd1

出现的效果却为

fd1,fd2,fd3
1,2,3
1,3,4
2,4,3
3,5,6
2,9,6
共有5行受到影响

却不是要求得到该效果:
fd1,fd2,fd3
1,2,3
2,4,3
3,5,6
共有3行受到影响


是否我这种做法不对?还是我写的这个
Select b.*
From (Select Distinct a.Fd1 As a_Distinct From tb1 a) c
Left Join tb1 b On c.a_Distinct = b.Fd1

语句不对?

有待高手指点?
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昵称被占用了 2008-11-11
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一句这样写

Select a.* 
From tb1 a
where not exists (
select 1 from tb1
where Fd1=a.Fd1
and (fd2<a.fd2
or fd2=a.fd2 and fd3<a.fd3)
)
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select id=identity(int,1,1),tb.* into # from tb order by fd1

select * from #

select fd1,fd2,fd3
from #
where id in(select min(id) from # group by fd1)

drop table #
fcuandy 2008-11-11
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http://topic.csdn.net/u/20080123/18/9731d130-0d4b-4c11-8d89-f2c3ca331f0c.html
昵称被占用了 2008-11-11
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你的想法错了,呵呵
moyifeng 2008-11-11
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--处理表重复记录(查询和删除)
/******************************************************************************************************************************************************
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
整理人:中国风(Roy)

日期:2008.06.06
******************************************************************************************************************************************************/

--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)

--> --> (Roy)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
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),方法3在SQl05时,效率高于1、2
方法1:
Select * from #T a where not exists(select 1 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 top 1 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(select 1 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 top 1 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


--> --> (Roy)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
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 #T a where exists(select 1 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 top 1 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(select 1 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 top 1 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


--> --> (Roy)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
select 1,N'A' union all
select 1,N'A' union all
select 1,N'A' union all
select 2,N'B' union all
select 2,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

(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(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

/*
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)
*/

jxydhzw 2008-11-11
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咦。CSDN的Bug好多哦。我只点了一下回复,发了二条。
jxydhzw 2008-11-11
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晕,这比较郁闷。。呵呵。上面那几位朋友贴出来的代码我之前也在这上面搜到看过。但是都比较复杂,麻烦,需要至少二个字段,而字段都是写死的。而我的是不固定的。客户需要查询某个表中是否有重复数据。就拿来运行。输入一张表,一个需去除重复字段,运行就可以了。客户是白痴型的。。
jxydhzw 2008-11-11
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晕,这比较郁闷。。呵呵。上面那几位朋友贴出来的代码我之前也在这上面搜到看过。但是都比较复杂,麻烦,需要至少二个字段,而字段都是写死的。而我的是不固定的。客户需要查询某个表中是否有重复数据。就拿来运行。输入一张表,一个需去除重复字段,运行就可以了。客户是白痴型的。。

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