SQL - Order by Max() on Alias

Question

I gather that I cannot get the MAX() on some alias that I have in the select statement in sql queries?

Example:

Select  
    CASE WHEN CompletionDate IS NOT NULL THEN DATEDIFF(d, CreatedDate, CompletionDate) ELSE NULL END AS DaysLong
from CombinedMastervw 
WHERE CreatedDate Between '03/01/2019 23:59:59.991' AND '04/01/2019 23:59:59.991'
ORDER BY MAX(dayslong)

Thus my question is on MAX(dayslong), do I have to end up doing a Max with the same code in the SELECT statement?

Answer 1

You should be able to use the alias.

Try:

ORDER BY dayslong

Max(dayslong) would return the single maximum value in the table you are selecting, so you cannot order by it.