使用CASE时无法对列别名进行ORDER BY

Question

I have a column that will show 'active' if the 'Expiration Date' in the empTable is < Current Date, and will show 'inactive' otherwise, then I want to sort that column so that all 'active' employees will be at the top.

CREATE PROCEDURE SOME_SP
@SortBy VARCHAR(10)
AS
SELECT emp.empname, 
CASE WHEN (emp.expiration_date < CURRENT_TIMESTAMP) THEN 'Active'   ELSE 'InActive' END AS Emp_Status, DeptName
FROM empTable emp, Dept dpt
WHERE emp.ID = dpt.ID
CASE @sortBy WHEN 'NAME' THEN emp.empName END,
CASE @sortBy WHEN 'STATUS' THEN Emp_Status END

If the user enter 'NAME', then the SP will sort by emp.empName , which works fine, but not the STATUS

I get an error saying that Invalid column name 'Emp_Status'

What did I do wrong?

Edited: I'm so sorry, I realize this query works if it is in plain SQL. However, the fact is I'm doing it in the Stored Procedure where the user can specify which column to sort. I will post a more complete SP above.

Answer 1

Okay, here are some comments that I have.

1 - Please get away from old style joins. Use the INNER JOIN ON clause.

2 - There is no reason why an alias can not be used in the ORDER BY clause. Please see Itzik Ben-Gans posting on logical processing order. The SELECT arguments are processed way before the ORDER BY.

http://www.sql.co.il/books/insidetsql2008/Logical%20Query%20Processing%20Poster.pdf

3 - Last but not least, a simple example (adventureworks) that make everyone with a hire date less than 2004 as Active, everyone else is in-active. This will sort by the status column.

Good luck.

John

-- Sample database
Use AdventureWorks2012
GO

-- Sample select showing alias works fine in a order by clause.
SELECT [LoginID] as login_id,
    CASE WHEN (e.HireDate < '20040101') THEN 'Active' 
    ELSE 'InActive' END AS emp_status
FROM [HumanResources].[Employee] as e
ORDER BY emp_status desc
GO

Since you changed your code above, here is a new answer to match. For a CASE statement on an ORDER BY you have to use the actual columns. For just a simple ORDER BY, the alias will work.

SO THE ANSWER is it ALL DEPENDS!!

Use AdventureWorks2012
GO

ALTER PROCEDURE usp_Sort_By_Column(@sort varchar(25))
AS
SELECT 
    [LoginID] as login_id,
    CASE WHEN (e.HireDate < '20040101') 
    THEN 'Active' ELSE 'InActive' END AS emp_status
FROM 
    [HumanResources].[Employee] as e
ORDER BY 
   (CASE 
       WHEN @sort = 'ID' THEN [LoginID] ELSE 
        (CASE WHEN (e.HireDate < '20040101') 
        THEN 'Active' ELSE 'InActive' END)
     END) 
GO

usp_Sort_By_Column 'STATUS'

Link to ORDER BY - Books On Line ...

http://msdn.microsoft.com/en-us/library/ms188385.aspx

Best answer for your crazy query: Make a sort column that is dynamic using the variable. Just order by the first column. Cleanest answer.

Use AdventureWorks2012
GO

ALTER PROCEDURE usp_Sort_By_Column(@sort varchar(25))
AS
SELECT 
    (CASE 
       WHEN @sort = 'ID' THEN [LoginID] ELSE 
        (CASE WHEN (e.HireDate < '20040101') 
        THEN 'Active' ELSE 'InActive' END)
     END) as Sort_Column,

    [LoginID] as login_id,
    CASE WHEN (e.HireDate < '20040101') 
    THEN 'Active' ELSE 'InActive' END AS emp_status
FROM 
    [HumanResources].[Employee] as e
ORDER BY 
   1
GO

usp_Sort_By_Column 'ID'