SQL Server ROW_NUMBER行为

Question

我有以下查询:

SELECT * FROM
(
    SELECT 
       a.TeacherID, a.UniversityID, 
       ROW_NUMBER() OVER (ORDER BY a.TeacherID) AS RowNum 
    FROM 
       SelectAll a  
    LEFT JOIN 
       mp_Ratings r ON a.TeacherID = r.TeacherID 
    GROUP BY 
       a.TeacherID, a.UniversityID
) AS TeacherInfo 
WHERE RowNum BETWEEN 10 AND 50

它工作正常.现在,如果我想做类似的事情:

SELECT * FROM
(
    SELECT 
       a.TeacherID, a.UniversityID, 
       ROW_NUMBER() OVER (ORDER BY a.TeacherID) AS RowNum 
    FROM 
       SelectAll a  
    LEFT JOIN 
       mp_Ratings r ON a.TeacherID = r.TeacherID 
    GROUP BY 
       a.TeacherID, a.UniversityID
) AS TeacherInfo 
WHERE RowNum BETWEEN 10 AND 50 AND UniversityID = 2

我什么也没得到,因为第2991UniversityID = 2行开始了.我希望能够重置每个不同的.Row_NumberUniversityID

我尝试了以下方法:

SELECT *, ROW_NUMBER() OVER (ORDER BY TeacherID) AS RowNum  
FROM
(
    SELECT 
        a.TeacherID, a.UniversityID 
    FROM 
        SelectAll a  
    LEFT JOIN 
        mp_Ratings r ON a.TeacherID = r.TeacherID 
    GROUP BY 
        a.TeacherID, a.UniversityID
) AS TeacherInfo 
WHERE UniversityID = 2

它row_numbers为每次搜索带来了新的一组,但如果我尝试使用RowNum别名:

SELECT *, ROW_NUMBER() OVER (ORDER BY TeacherID) AS RowNum  
FROM
(
    SELECT 
        a.TeacherID, a.UniversityID 
    FROM 
        SelectAll a  
    LEFT JOIN 
        mp_Ratings r ON a.TeacherID = r.TeacherID 
    GROUP BY 
        a.TeacherID, a.UniversityID
) AS TeacherInfo 
WHERE UniversityID = 2 
  AND RowNum BETWEEN 10 AND 20

我明白了

消息207,级别16,状态1,行4无效的列名称'RowNum'.

我的选择出了什么问题？为什么我不能访问RowNum别名？

Answer 1

您只需将WHERE子句移动到内部查询.

SELECT TeacherID, UniversityID, RowNum FROM
(
    SELECT a.TeacherID, a.UniversityID, ROW_NUMBER() OVER 
     (ORDER BY a.TeacherID) AS RowNum FROM SelectAll a
     LEFT JOIN mp_Ratings r 
     ON a.TeacherID = r.TeacherID 
     WHERE UniversityID = 2
     GROUP BY a.TeacherID, a.UniversityID
) as TeacherInfo WHERE RowNum BETWEEN 10 AND 50;

您无法访问RowNum查询外部版本中的别名,因为别名尚不存在.SELECT在之前解析倒数第二个ORDER BY.WHERE之前处理过SELECT.