[hibernate-dev] SQM - alias registry

[Steve Ebersole]

>
> > Here the aliases `c` do infringe.  In the subquery, we don't really know
> > which reference the `c` alias should resolve to.  We *could* here
> assuming
> > that the subquery is uncorrelated.  Bu without this rule we really would
> > not know that the subquery is correlated
>
> Out of curiosity, Couldn't for this case assume that the second alias
> overrides the first.
> This might cause some hard to spot errors, though.
>

The issue really is for cases of correlated subqueries (where the subquery
refers to the outer query).  So imagine a query such as:

select ...
from Salesperson s
where exists (
    select count(*)
    from Sale s2
    where s.id = s2.salesperson.id ...
    group by s2.salesperson.id
    having count(*) > :sales
)

So here the predicate `s.id = s2.salesperson.id` defines a correlation
beween hthe queries.  If we allowed the "alias overriding", it is quite
possible for the user to (mistakenly) write this query as:

select ...
from Salesperson s
where exists (
    select count(*)
    from Sale s
    where s.id = s.salesperson.id ...
    group by s.salesperson.id
    having count(*) > :sales
)

Which validates fine, but is not *really* what they meant and would not
return what they are looking for.