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服务器之家 - 编程语言 - ASP.NET教程 - sqlserver 删除重复记录处理(转)

sqlserver 删除重复记录处理(转)

2019-09-17 13:23asp.net之家 ASP.NET教程

删除重复记录有大小关系时,保留大或小其中一个记录

注:此处“重复”非完全重复,意为某字段数据重复 
  HZT表结构 
ID int 
Title nvarchar(50) 
AddDate datetime 
  数据 
一. 查找重复记录 
  1. 查找全部重复记录 
Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1) 

2. 过滤重复记录(只显示一条) 
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title) 
注:此处显示ID最大一条记录 
二. 删除重复记录 
  1. 删除全部重复记录(慎用) 
Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1) 

  2. 保留一条(这个应该是大多数人所需要的) 
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title) 
  注:此处保留ID最大一条记录 

其它相关:

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)
*/

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