Re: join-performance problem

Wolfgang(dot)Fuertbauer(at)ebewe(dot)com writes:
>> explain SELECT b.Kdnr, date_part('year', b.Datum), d.Name, e.Name, a.Menge,
>> a.Rabproz, a.Netto - (a.netto * a.rabproz / 100),
>> a.Netto * b.kurs - ((a.netto * b.kurs) * a.rabproz / 100), 'RG'
>> FROM Faktzeilen a, Fakt b, Artikel c, Kollektion d, ArGruppen e
>> where a.Fanr = b.nr
>> and c.nr = a.Arnr
>> and c.Kollektion = d.Nr
>> and (c.Gruppe = e.nr or c.gruppe = 0)
>> and b.kdnr = 49736;

Anyplace that c.gruppe is 0, this is an unconstrained join to e --- ie,
you'll get a row out for *every* row of e. Somehow I doubt that's the
behavior you really want.

I concur with Stephan's observation that you haven't analyzed. But
even when you have, this query doesn't give much traction for the use
of indexes on a --- the only constraint that might possibly be used to
avoid a complete scan of a is the "b.kdnr = 49736", and that's not even
on a. The only hope I can see is if you create an index on b.kdnr;
then (if there aren't very many rows matching b.kdnr = 49736), it might
be able to pick those up with an indexscan on b and then do an inner
indexscan join to a using a.Fanr = b.nr. Your secondary indexes on a
look like wastes of space (at least for this query).

regards, tom lane