Re: Query optimization path

On Sun, 12 Jan 2003, Gaetano Mendola wrote:

> "Bruno Wolff III" <bruno@wolff.to> wrote in message
> news:20030112170108.GB31080@wolff.to...
> >   Gaetano Mendola <mendola@bigfoot.com> wrote:
> > > Hi all,
> > >
> > > I have the following query:
> > >
> > > SELECT count(1)
> > > FROM providers p JOIN class_default cd    USING (id_provider)
> > >                  JOIN user_data     ud    USING (id_class)
> > >                  JOIN v_user_traffic ut   USING (id_user)
> > > WHERE id_user_status in (4,5) AND
> > >       p.company = 'XXXXX';
> > >
> > > is not slow but I notice that if I do explain analyze with the table
> > > reordered
> > > inside the select in another way the cost change.
>
> > Using "JOIN" fixes the order that tables are joined in. If you are
> > just doing inner joins, then you probably don't want to use the "JOIN"
> > keyword. The exception being when there are so many tables being joined
> > that you want to manually specify at least some of the join ordering in
> > order to help out the planner.
>
> And where is written this behavior ? Is it SQL standard ?

http://www.postgresql.org/idocs/index.php?explicit-joins.html

The standard generally has nothing to say about optimization.