注：此處“重復”非完全重復,意為某字段數(shù)據(jù)重復
HZT表結(jié)構(gòu)
ID int
Title nvarchar(50)
AddDate datetime
數(shù)據(jù)
一. 查找重復記錄
1. 查找全部重復記錄
Select * From 表 Where 重復字段 In (Select 重復字段 From 表 Group By 重復字段 Having Count(*)>1)
2. 過濾重復記錄(只顯示一條)
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
注：此處顯示ID最大一條記錄
二. 刪除重復記錄
1. 刪除全部重復記錄（慎用）
Delete 表 Where 重復字段 In (Select 重復字段 From 表 Group By 重復字段 Having Count(*)>1)
2. 保留一條（這個應(yīng)該是大多數(shù)人所需要的）
Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
注：此處保留ID最大一條記錄
其它相關(guān):
刪除重復記錄有大小關(guān)系時,保留大或小其中一個記錄
--> --> (Roy)生成測試數(shù)據(jù)
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最小的記錄(推薦用1,2,3),保留最小一條
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為唯一時可用):
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
生成結(jié)果:
/*
ID Name Memo
----------- ---- ----
1 A A1
4 B B1
(2 行受影響)
*/
--II、Name相同ID保留最大的一條記錄:
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為唯一時可用):
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 行受影響)
*/
--3、刪除重復記錄沒有大小關(guān)系時，處理重復值
--> --> (Roy)生成測試數(shù)據(jù)
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--排除重復記錄結(jié)果集生成臨時表#
truncate table #T--清空表
insert #T select * from # --把臨時表#插入到表#T中
--查看結(jié)果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影響)
*/
--重新執(zhí)行測試數(shù)據(jù)后用方法2
方法2:
alter table #T add ID int identity--新增標識列
go
delete a from #T a where exists(select 1 from #T where Num=a.Num and Name=a.Name and ID>a.ID)--只保留一條記錄
go
alter table #T drop column ID--刪除標識列
--查看結(jié)果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影響)
*/
--重新執(zhí)行測試數(shù)據(jù)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
--查看結(jié)果
select * from #T
/*
Num Name
----------- ----
1 A
2 B
(2 行受影響)
*/
