SQL Server2008中刪除反復記載的辦法分享。本站提示廣大學習愛好者：（SQL Server2008中刪除反復記載的辦法分享）文章只能為提供參考，不一定能成為您想要的結果。以下是SQL Server2008中刪除反復記載的辦法分享正文
如今讓我們來看在SQL SERVER 2008中若何刪除這些記載, 起首,可以模仿造一些簡略反復記載:
Create Table dbo.Employee (
[Id] int Primary KEY ,
[Name] varchar(50),
[Age] int,
[Sex] bit default 1
)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(1,'James',25,default)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(2,'James',25,default)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(3,'James',25,default)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(4,'Lisa',24,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(5,'Lisa',24,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(6,'Lisa',24,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(7,'Mirsa',23,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(8,'Mirsa',23,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(9,'Mirsa',23,0)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(10,'John',26,default)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(11,'Abraham',28,default)
Insert Into Employee ([Id] , [Name] , [Age] , [Sex] ) Values(12,'Lincoln',30,default)
OK,起首我們應用最多見的辦法:
Delete From Employee Where Name in (select NameFrom Employee Group By Name Having Count(Name)>1);
接著應用RowNumber():
Delete T From( Select Row_Number() Over(Partition By [Name] Order By (SELECT 0)) As RowNumber,* From Employee) TWhere T.RowNumber > 1;
還可使用CTE (Common Table Expressions):
With Dups as
(
select ROW_NUMBER() Over(Partition by [Name] Order by (SELECT 0)) as rn
FROM Employee
)
Delete From Dups
Where rn>1;
再加上RANK()的CTE:
WITH Dups As
(
Select [ID],[Name],[Age],[Sex]
, ROW_NUMBER() OVER(Partition By [Name] Order By (SELECT 0)) AS rn
,RANK() OVER(Partition By [Name] Order By (SELECT 0)) AS rnk
FROM Employee
)
DELETE FROM Dups
WHERE rn<>rnk;
上面是這四個T-SQL查詢的履行籌劃:
你可以看到沒有效CTE的辦法開支最年夜, 重要是在Table Spool, 這裡開支了44%, Table Spool 是一個物理運算符。
Table Spool 運算符掃描輸出，並將各行的一個正本放入隱蔽的假脫機表中，此表存儲在 tempdb 數據庫中而且僅在查詢的生計期內存在。假如重繞該運算符（例如經由過程 Nested Loops 運算符重繞），但不須要任何從新綁定，則將應用假脫機數據，而不消從新掃描輸出。
留意下面的辦法只是在反復記載比擬少的情形下, 假如反復記載多. DELETE將會異常慢, 最好的辦法是復制目的數據到另外一個新表,刪除本來的表,重定名新表為本來的表. 或用暫時表, 如許還可以削減數據庫事務日記. 看上面的T-SQL:
WITH Dups As
(
Select [ID],[Name],[Age],[Sex]
, ROW_NUMBER() OVER(Partition By [ID] Order By (SELECT 0)) AS rn
FROM Employee
)
Select [ID],[Name],[Age],[Sex]
INTO dbo.EmployeeDupsTmp
FROM Dups
WHERE rn=1
DROP TABLE dbo.Employee;
EXEC sp_rename 'dbo.EmployeeDupsTmp','Employee'
願望這篇POST對您開辟有贊助.作者：Petter Liu
