row_number() over () as row_number

时间: 2023-11-28 09:46:30 浏览: 165

SQL ROW_NUMBER()分页比较

SQL ROW_NUMBER() 分页比较在 SQL Server 2005 中，使用 ROW_NUMBER() 函数可以实现分页功能，这种方法相比于 SQL Server 2000 中的分页方式效率要高出很多。但是，很多人在使用 ROW_NUMBER() 函数时，使用的方法并不正确。在本文中，我们将介绍使用 ROW_NUMBER() 函数的正确方法，并进行性能比较。我们需要创建一个示例表和索引，并初始化 100 万条数据： ```sql CREATE TABLE [dbo].[Users]( [ID] [int] IDENTITY(1,1) NOT NULL, [Name] [varchar](50) NULL, [test] [nchar](10) NULL, CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED ( [ID] ASC ) ON [PRIMARY] ) ON [PRIMARY] CREATE UNIQUE NONCLUSTERED INDEX [Inx_Name] ON [dbo].[Users] ( [Name] ASC ) ON [PRIMARY] DECLARE @index INT SET @index=0 WHILE @index<1000000 BEGIN INSERT INTO Users(Name,test) values(@index,'walkingp') SET @index = @index + 1 END ``` 接下来，我们将介绍两种使用 ROW_NUMBER() 函数的方法：不正确的使用方式和正确的使用方式。不正确的使用方式是先查出所有数据，然后再排序： ```sql select Id,Name,test from ( select row_number() over(order by name) as rowNum,* from users ) as t where rowNum between 5000 and 5100 ``` 这种方法的缺点是需要查出所有数据，然后再进行排序和过滤，这将导致性能问题。正确的使用方式是先查出主键进行排序和过滤，然后使用过滤后的主键来查找数据： ```sql select a.Id,a.Name,a.test from users as a inner join ( select rowNum,id from ( select row_number() over(order by name) as rowNum,ID from users ) as t where rowNum between 4000 and 4100 ) as b on a.id = b.id order by b.rownum ``` 这种方法的优点是可以避免查出所有数据，只需要查出需要的数据，从而提高性能。下面是两种方法的性能比较： ```sql set statistics io on set statistics time on go print 'Error.5000-------------------------' declare @time datetime declare @ms int set @time= getdate() select Id,Name,test from ( select row_number() over(order by name) as rowNum,* from users ) as t where rowNum between 5000 and 5100 set @ms=datediff(ms,@time,getdate()) print @ms--毫秒数 go print 'Right.5000-------------------------' declare @time datetime declare @ms int set @time= getdate() select a.Id,a.Name,a.test from users as a inner join ( select rowNum,id from ( select row_number() over(order by name) as rowNum,ID from users ) as t where rowNum between 4000 and 4100 ) as b on a.id = b.id order by b.rownum set @ms=datediff(ms,@time,getdate()) print @ms--毫秒数 go print 'Error.500000-------------------------' declare @time datetime declare @ms int set @time= getdate() select Id,Name,test from ( select row_number() over(order by name) as rowNum,* from users ) as t where rowNum between 500000 and 501000 set @ms=datediff(ms,@time,getdate()) print @ms--毫秒数 ``` 从结果可以看到，使用正确的方法可以显著提高性能。

row_number() over()是一种在SQL Server中用于对结果集进行排序并为每一行分配一个唯一的行号的函数。它可以用于分页查询、删除重复行等操作。以下是一个使用row_number() over()函数的例子： ```sql SELECT ROW_NUMBER() OVER(ORDER BY id) as row_number, name, age FROM students ``` 这个查询将会返回一个结果集，其中包含每个学生的姓名、年龄和一个唯一的行号。行号将按照id列的升序排列。

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row_number() over () as row_number

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