使用CASE WHEN时ORDER BY不工作，但没有它可以工作吗？

Question

我有以下select语句，我试图以特定的方式排序我的结果，特别是部门的层次结构。但是，当我添加案例时，我的ORDER BY停止工作并给我一个错误：

如果语句包含UNION，INTERSECT或EXCEPT运算符，则ORDER BY项必须出现在选择列表中。

我不知道为什么会这样，因为我在每个SELECT语句中选择all。

Select * FROM AccountAdminTable Where CollegeCode = 'A10' AND AdminLevel LIKE 'Account Administrator'
Union
Select * FROM AccountAdminTable Where CollegeCode = 'A10' AND AdminLevel LIKE 'Department Head/Director'
Union
Select * FROM AccountAdminTable Where CollegeCode = 'A10' AND AdminLevel LIKE 'Dean/Vice President'
Order By AdminLevel ASC

这不起作用：

Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Account Administrator'
Union
Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Department Head/Director'
Union
Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Dean/Vice President'
Order By Case
    When AdminLevel = 'Account Administrator' Then 1
    When AdminLevel = 'Department Head/Director' Then 2
    When AdminLevel = 'Dean/Vice President' Then 3
    Else 4 End ASC

任何帮助是极大的赞赏！以下是一些示例数据。

College Code| AdminLevel               | Name
A           | Account Administrator    | Bob
A           | Department Head/Director | Tim
A           | Dean/Vice President      | Jeff
B           | Account Administrator    | Gary
B           | Department Head/Director | Phil
B           | Dean/Vice President      | John
C           | Account Administrator    | Bill
C           | Account Administrator    | Larry

Answer 1

你有2个选择：

• 使用派生表在ORDER BY中使用CASE。

SELECT *
FROM(
         Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Account Administrator'
        Union
        Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Department Head/Director'
        Union
        Select * FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Dean/Vice President'
        )t
Order By Case 
        When AdminLevel = 'Account Administrator' Then 1
        When AdminLevel = 'Department Head/Director' Then 2
        When AdminLevel = 'Dean/Vice President' Then 3
        Else 4 End ASC;

*或添加定义订单的列。

Select *, 1 AS OrderCol FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Account Administrator'
Union
Select *, 2 AS OrderCol FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Department Head/Director'
Union
Select *, 3 AS OrderCol FROM AccountAdminTable Where CollegeCode = 'A' AND AdminLevel LIKE 'Dean/Vice President'
Order By OrderCol;

无论哪种方式，您可能希望将UNION更改为UNION ALL以提高性能。除非你真的消除重复。

Answer 2

你知道，你真的根本不需要使用UNION。由于您的所有SELECTS都来自同一个表，您可以这样做（注意，下面我的伪代码中使用的缩写。显然，在代码中使用正确的值）：

Select * FROM AccountAdminTable 
Where CollegeCode = 'A'
AND AdminLevel IN ('Account Administrator','Dept HD','Dean/VP')
ORDER BY CASE {Your CASE Expression}

Answer 3

编写查询的另一个选项是：

SELECT AccountAdminTable.*
FROM AccountAdminTable
INNER JOIN (VALUES
    (1, 'Account Administrator'),
    (2, 'Dept HD'),
    (3, 'Dean/VP')
) AS vlist(Sort, AdminLevel) ON AccountAdminTable.AdminLevel = vlist.AdminLevel
WHERE CollegeCode = 'A'
ORDER BY vlist.Sort

或者更好的是，为管理级别创建一个表并通过外键引用它。