How do I perform a GROUP BY on an aliased column in MS-SQL Server?

Question

I\'m trying to perform a group by action on an aliased column (example below) but can\'t determine the proper syntax.

SELECT       LastName + \', \'         


        

Answer 1

You can use CROSS APPLY to create an alias and use it in the GROUP BY clause, like so:

SELECT       FullName
FROM         Customers
CROSS APPLY  (SELECT LastName + ', ' + FirstName AS FullName) Alias
GROUP BY     FullName

Answer 2

You pass the expression you want to group by rather than the alias

SELECT       LastName + ', ' + FirstName AS 'FullName'
FROM         customers
GROUP BY      LastName + ', ' + FirstName

Answer 3

If you want to avoid the mess of the case statement being in your query twice, you may want to place it in a User-Defined-Function.

Sorry, but SQL Server would not render the dataset before the Group By clause so the column alias is not available. You could use it in the Order By.

Answer 4

Unfortunately you can't reference your alias in the GROUP BY statement, you'll have to write the logic again, amazing as that seems.

SELECT       LastName + ', ' + FirstName AS 'FullName'
FROM         customers
GROUP BY     LastName + ', ' + FirstName

Alternately you could put the select into a subselect or common table expression, after which you could group on the column name (no longer an alias.)

Answer 5

Given your edited problem description, I'd suggest using COALESCE() instead of that unwieldy CASE expression:

SELECT FullName
FROM (
  SELECT COALESCE(LastName+', '+FirstName, FirstName) AS FullName
  FROM customers
) c
GROUP BY FullName;

Answer 6

This is what I do.

SELECT FullName
FROM
(
  SELECT LastName + ', ' + FirstName AS FullName
  FROM customers
) as sub
GROUP BY FullName

---

This technique applies in a straightforward way to your "edit" scenario:

SELECT FullName
FROM
(
  SELECT
     CASE
       WHEN LastName IS NULL THEN FirstName
       WHEN LastName IS NOT NULL THEN LastName + ', ' + FirstName
     END AS FullName
  FROM customers
) as sub
GROUP BY FullName