Why can't I use alias in a count(*) “column” and reference it in a having clause?

Question

I was wondering why can\'t I use alias in a count(*) and reference it in the having clause. For instance:

select Store_id as StoreId, count(*) as _count
             


        

Answer 1

Probably because that's the way sql defines the namespaces. take, for example:

  select a as b, b as a
    from table
   where b = '5'
order by a

what do a and b refer to? The designers just chose to make the aliases only appear on the "outside" of the query.