group by - problem in MsSQL

[Anon]

Hi all,
Iam use to MySQL database and new to MsSQL
I found alot of differnces in MsSQL syntax
In MsSQL, i need to group by the aliases on coulmn names,but this is not allowed here why?
like my query is:

select age as abc,salary as sal from test group by abc,sal order by age desc;
when i run this query i get an error

here the error that comes is
"invalid coulmn name abc"
"invalid coulmn name sal"
could anyone tell me where iam wrong?
how do i group in this case?
is grouping on the aliases of the coulmn nam eis allowed ?

Regards
Roopa