> Hello!
>
> Vadim already gave the idea to use EXISTS. Will try it.
> Thanks to all who replied!
>
> On Wed, 10 Mar 1999, Jackson, DeJuan wrote:
> > Try your query this way:
> > SELECT DISTINCT subsec_id
> > FROM positions p
> > WHERE EXISTS(SELECT 1
> > FROM central c, shops s, districts d
> > WHERE p.pos_id = c.pos_id AND
> > c.shop_id = s.shop_id AND
> > s.distr_id = d.distr_id AND
> > d.city_id = 2);
>
> > Make sure you have indexes on pos_id, shop_id, distr_id,
> and city_id.
>
> All these are primary keys in corresponding tables, and hence have
> UNIQUE indicies. Is it enough?
>
> Oleg.
You should have indexes on both the primary and the referenced table.
(i.e. positions.pos_id and central.pos_id) It gives PostgreSQL more
options on which join methods to use while still having an index to
reference.
-DEJ