Thank you all very much. This "official" forum is really great. 2009/11/19 Oliveiros C, <oliveiros.crist...@marktest.pt>
> Howdy, > > It is quite simple, the joins you used would output a long list of > pairs (client,computer), and, as many people has more than one computer, > many clients will appear repeated, but the COUNT keyword will count them > more than once though. > > The DISTINCT keyword prevents one client from appearing more than once... > > It's basically that... > > Hope this helped > > Best, > Oliveiros > > > ----- Original Message ----- > *From:* Another Trad <anothert...@gmail.com> > *To:* Oliveiros C, <oliveiros.crist...@marktest.pt> > *Cc:* pgsql-sql@postgresql.org > *Sent:* Wednesday, November 18, 2009 5:37 PM > *Subject:* Re: [SQL] need nelp with aggregate functions > > ok, I did: SELECT count(DISTINCT c.cliente_id) as > qtd_client,count(cm.cm_id) as qtd_computers > GREAT. It works. > Please, explain me why and how it works, I wanna learn and do by myself > next time :) > > > 2009/11/18 Oliveiros C, <oliveiros.crist...@marktest.pt> > >> Try substituting the SELECT count(c) as qtd_client,count(cm) as >> qtd_computers >> >> by >> >> SELECT count( DISTINCT c.cliente_id) as qtd_client,count(/* put here the >> primary key of the computer table */ ) as qtd_computers >> >> Then tell me if it output what you want >> >> Best, >> Oliveiros >> >> >> ----- Original Message ----- >> *From:* Another Trad <anothert...@gmail.com> >> *To:* pgsql-sql@postgresql.org >> *Sent:* Wednesday, November 18, 2009 4:55 PM >> *Subject:* [SQL] need nelp with aggregate functions >> >> The DB structure is in attachment. >> I with the number of clients and the number of computers that have >> processors with "manufacturer" = "INTEL" and "speed" = "2GB" >> I am trying: >> >> select count(c) as qtd_client, count(cm) as qtd_computers >> >> >> from cliente c >> inner JOIN computer cm on (c.cliente_id = cm.cliente_id) >> inner join processor p on (cm.processor_id = p.processor_id) >> inner join speed s on (s.speed_id = p.speed_id) >> INNER JOIN manufacturer m on (p.manufacturer_id=m.manufacturer_id) >> >> >> where m.manufacturer = 'INTEL' >> and s.speed = '2GB' >> >> but is not working >> anyone can help me? >> >> ------------------------------ >> >> >> -- >> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-sql >> >> >
