SQL存储过程问题

我对以下存储过程有问题

CREATE PROCEDURE LockRoots
    -- Add the parameters for the stored procedure here
    @lock uniqueidentifier,
    @count int
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    UPDATE R
    SET R.[Lock] = @lock
    FROM 
    (
        SELECT TOP @count *
        FROM [Root] as R
        --LEFT JOIN [Container] as C ON R.ID = C.RootID
        WHERE [Lock] IS NULL
        --ORDER BY NEWID()
    );
END
GO

“选择TOP@count*”出现问题，为什么我不能“选择TOP@variablemount”记录？

注意：另外，SQL Server 2005+用于参数化的TOP

的可能重复项

...
SELECT TOP (@count) *
...