Subject Re: Subselect vs. JOIN
Author Nico Callewaert <>
Thanks Ann,

regards? Nico

--- In, "Ann W. Harrison"
<aharrison@i...> wrote:
> At 11:18 AM 12/10/2002 +0000, Nico Callewaert <nico-
callewaert@p...> wrote:
> >Hi,
> >
> >I was hoping to find a already posted answer in this group, but it
> >seems not. The question is : I wonder when it's better to use a
> >subselect or a join ? When I need only 1 field from a table I
> >a subselect, when I use several fields I use a join. Is that
> >correct ? Because I think in a subselect you can only get 1
> >field ? I wonder which one is the most performant ?
> Generally, using FB1, a join is faster. However, to emulate
> some subselects, you need to use an outer join - preserving the
> primary table when the secondary table has no match. Outer
> join optimization is .... suboptimal. If you do more than
> one subselect on the same record, Firebird will go through all
> the steps to find the record again, however, all the pages
> referenced should be in cache, so the second lookup is very
> cheap. Well, very cheap compared to the first one.
> Regards,
> Ann
> We have answers.