sql 删除数据,该怎么处理

sql 删除数据
在SQL数据库中删除多条重复记录 求解

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SQL code

--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 #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 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           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=@Name    set 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)*/
[解决办法]
SQL code
DECLARE @T TABLE(ID int)INSERT @T SELECT 1INSERT @T SELECT 1INSERT @T SELECT 1DELETE tFROM (SELECT *,row=ROW_NUMBER()OVER( PARTITION BY  ID ORDER BY ID) FROM @T)tWHERE row>1SELECT * FROM @T/*1*/
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在SQL数据库中删除多条重复记录 求解

[解决办法]
SQL code
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 #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.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    A35           B    B2(2 行受影响)*/