On Wed, 23 Oct 2002, Tomasz Myrta wrote:
> Uz.ytkownik Stephan Szabo napisa?:
> > Does using X.group_id=3 in the where clause work better?
> It works better, but not if you want to create a view and make
> "select * from some_view where group_id=3" :-(
But you can't do that anyway, because you don't expose group_id
in the original query. I assume user_id was a mistake then and was
meant to be group_id or that both were meant to be in the
select list.
I see these two queries that in 7.3 push the clause into the
subquery and I believe should have the same output:
create view v as
select group_id, a/sum_a as percent_a, b/sum_b as percent_b
from (select group_id, sum(a) as sum_a, sum(b) as sum_b from users group by group_id) X join users using
(group_id);
and
create view v as
select X.group_id, a/sum_a as percent_a, b/sum_b as percent_b
from users join (select group_id, sum(a) as sum_a, sum(b) as sum_b from users group by group_id) X on
(X.group_id=users.group_id);
In the first case changing the order means that the output
group_id column is X.group_id rather than users.group_id
(using removes one of them which is why group_id isn't
ambiguous. In the second it uses on to get both group_ids
and exposes the one from X.
> > On 7.3 with no statistics for the table, that appears
> > to move the filter into the subquery plan rather than the
> > outer users scan.
> Do you mean the second query will work on 7.3?
No, the case of setting X.group_id.
