如何使用多个表的“选择行号（）”

Question

我尝试使用ROW_NUMBER()子句检索特定的行号

当我执行此查询时

SELECT 
student.Aca_num,id_num,student.name,dob,pic,class.name,
student.tell,student.mobile1,mobile2,student.Email,nach.name,dist,notes
FROM
student,[user],users_classes,class,nach
WHERE
((class.ID)=student.class)
and
((nach.ID)=student.nach)
and
((student.class)=users_classes.Class_ID)
AND
((users_classes.[User_ID])=[user].ID)
AND
(([user].ID)=3)

现在我需要在此查询中使用Row Number()，只通过指定行号来检索一行。

我使用Row Number()像这样

SELECT * FROM
    (SELECT ROW_NUMBER() OVER (ORDER BY name) AS Row, * FROM Student) AS EMP
WHERE Row = 3

此查询返回学生表的third行

但将Row Number()与多个表格（例如（学生，班级）

）一起使用时出错

SELECT * FROM
    (SELECT ROW_NUMBER() OVER (ORDER BY student.name) AS Row, * FROM Student,Class) AS EMP
WHERE Row = 3

它给了我这个错误

  

Msg 8156，Level 16，State 1，Line 10 The column＆＃39; Name＆＃39;被指定了   多次为EMP＆＃39;。

如何使用多个Table的Row Number()子句返回特定的行号|

提前致谢

问候......

Answer 1

这与ROW_NUMBER()没有任何关系。

在Student和Class表格中，您都有一个名为Name的列。创建子查询时，结果集中的列名必须是不同的。

所以不要使用*，明确命名列，包括（如果你必须有两个名字）一个别名：

SELECT * FROM
    (SELECT ROW_NUMBER() OVER (ORDER BY s.name) AS Row, s.Name as StudentName,c.Name as ClassName FROM Student s,Class c) AS EMP
WHERE Row = 3

当然，目前，你正在两张桌子之间进行笛卡尔连接。您更有可能以某种方式加入表格，例如

... FROM Student s INNER JOIN Class c on s.class = c.id ...

Answer 2

我希望这很有用;

;WITH Emp AS
(
            -- Avoid using reserved words like [Row] (changed to nRow)
    SELECT   ROW_NUMBER() OVER (ORDER BY student.name) AS nRow 
            -- You cannot use * because your tables have columns with matching names
            -- Make sure that the columns you require are unique in their name or are aliased
            -- to be unique
            ,S.Col AS Foo
            ,C.Col AS Bar 
    FROM Student    S
    --  Your FROM expression [FROM Student,Class] will result effectively in a CROSS JOIN
    --  Clarify your join condition if you do not want a cartesian product
    JOIN Class      C ON S.Col = C.Col
)
SELECT *
FROM Emp
WHERE nRow = 3