sqlserver 删除重复记录处理（转）_实用技巧

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 nulldrop table #TGoCreate table #T([ID] int,[Name] nvarchar(1),[Memo] nvarchar(2))Insert #Tselect 1,N'A',N'A1' union allselect 2,N'A',N'A2' union allselect 3,N'A',N'A3' union allselect 4,N'B',N'B1' union allselect 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  A14      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.IDwhere 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  A35      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 nulldrop table #TGoCreate table #T([Num] int,[Name] nvarchar(1))Insert #Tselect 1,N'A' union allselect 1,N'A' union allselect 1,N'A' union allselect 2,N'B' union allselect 2,N'B'Go

方法1:if object_id('Tempdb..#') is not nulldrop 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      A2      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godelete 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goalter table #T drop column ID--删除标识列

--查看结果select * from #T

/*Num     Name----------- ----1      A2      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 forselect count(1)-1,Num,Name from #T group by Num,Name having count(1)>1declare @con int,@Num int,@Name nvarchar(1)open Roy_Cursorfetch next from Roy_Cursor into @con,@Num,@Namewhile @@Fetch_status=0begin set rowcount @con;delete #T where Num=@Num and Name=@Nameset rowcount 0;fetch next from Roy_Cursor into @con,@Num,@Nameendclose Roy_Cursordeallocate Roy_Cursor

--查看结果select * from #T/*Num     Name----------- ----1      A2      B

(2 行受影响)*/

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