exec sp_executesql N'SELECT TOP (10) 

    [Project1].[ID] AS [ID], 

    [Project1].[UID] AS [UID], 

    [Project1].[Name] AS [Name], 

    [Project1].[Email] AS [Email], 

    [Project1].[Title] AS [Title], 

    [Project1].[Content] AS [Content], 

    [Project1].[ImageSrc] AS [ImageSrc], 

    [Project1].[ThImageSrc] AS [ThImageSrc], 

    [Project1].[IP] AS [IP], 

    [Project1].[PostDateTime] AS [PostDateTime], 

    [Project1].[UpdateDateTime] AS [UpdateDateTime], 

    [Project1].[ForumID] AS [ForumID], 

    [Project1].[ParentID] AS [ParentID]

    FROM ( SELECT [Project1].[ID] AS [ID], [Project1].[UID] AS [UID], [Project1].[Name] AS [Name], [Project1].[Email] AS [Email], [Project1].[Title] AS [Title], [Project1].[Content] AS [Content], [Project1].[ImageSrc] AS [ImageSrc], [Project1].[ThImageSrc] AS [ThImageSrc], [Project1].[IP] AS [IP], [Project1].[PostDateTime] AS [PostDateTime], [Project1].[UpdateDateTime] AS [UpdateDateTime], [Project1].[ForumID] AS [ForumID], [Project1].[ParentID] AS [ParentID], row_number() OVER (ORDER BY [Project1].[UpdateDateTime] DESC) AS [row_number]

        FROM ( SELECT 

            [Extent1].[ID] AS [ID], 

            [Extent1].[UID] AS [UID], 

            [Extent1].[Name] AS [Name], 

            [Extent1].[Email] AS [Email], 

            [Extent1].[Title] AS [Title], 

            [Extent1].[Content] AS [Content], 

            [Extent1].[ImageSrc] AS [ImageSrc], 

            [Extent1].[ThImageSrc] AS [ThImageSrc],  

            [Extent1].[IP] AS [IP], 

            [Extent1].[PostDateTime] AS [PostDateTime], 

            [Extent1].[UpdateDateTime] AS [UpdateDateTime], 

            [Extent1].[ForumID] AS [ForumID], 

            [Extent1].[ParentID] AS [ParentID]

            FROM [dbo].[Thread] AS [Extent1]

            WHERE ([Extent1].[ForumID] = @p__linq__0) AND (@p__linq__0 IS NOT NULL) AND ([Extent1].[ParentID] IS NULL)

        )  AS [Project1]

    )  AS [Project1]

    WHERE [Project1].[row_number] > 100

    ORDER BY [Project1].[UpdateDateTime] DESC',N'@p__linq__0 int',@p__linq__0=4

这是用ENTITY FRAMEWORK生成的SQL语句，发现很慢：
SQL Server 分析和编译时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。

SQL Server 执行时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。
SQL Server 分析和编译时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。
SQL Server 分析和编译时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。

(10 行受影响)
表 'Thread'。扫描计数 50，逻辑读取 2280 次，物理读取 0 次，预读 0 次，lob 逻辑读取 0 次，lob 物理读取 0 次，lob 预读 0 次。
表 'Worktable'。扫描计数 0，逻辑读取 0 次，物理读取 0 次，预读 0 次，lob 逻辑读取 0 次，lob 物理读取 0 次，lob 预读 0 次。
表 'Worktable'。扫描计数 0，逻辑读取 0 次，物理读取 0 次，预读 0 次，lob 逻辑读取 0 次，lob 物理读取 0 次，lob 预读 0 次。

(1 行受影响)

SQL Server 执行时间:
CPU 时间 = 3816 毫秒，占用时间 = 1528 毫秒。

SQL Server 执行时间:
CPU 时间 = 3816 毫秒，占用时间 = 1528 毫秒。
SQL Server 分析和编译时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。

SQL Server 执行时间:
CPU 时间 = 0 毫秒，占用时间 = 0 毫秒。




但是如果将[Project1].[row_number] > 100改成[Project1].[row_number] > 0则查询变得很快，或者在SQL语句中随便加入一个空格也会变的很快，这是什么原因？
这是正常状态下的执行计划：