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UniversityID = 2开始于行号 2991 。我希望能够使用每个不同的Row_Number重置UniversityID。

我尝试了以下内容：

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

为每次搜索带来了新的row_numbers，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

我得到了

消息207，级别16，状态1，行4无效的列名称'RowNum'。

我的选择有什么问题？为什么我无法访问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;

您无法访问查询外部版本中的RowNum别名，因为别名尚不存在。在SELECT之前，ORDER BY被解析为倒数第二。在WHERE之前处理SELECT。

Answer 2

在row_number上使用分区：

row_number() over(partition by UniversityID, order by teacherid)

SQL Server ROW_NUMBER行为

2 个答案: