>As a follow-up, the "why" is becuase the result (with the alias name) hasn't been created.....
>
>That's why you can use expression aliases in an ORDER BY....becuase the result set has already been created (sort of), and the database engine can refer to any alias names. But prior to that (i.e. in a GROUP BY), it's too early to use aliases.

One more example of the exact same problem, BTW:

http://forums.asp.net/p/1426450/3187277.aspx#3187277