Re: "left join" not working?

From: msi77 <msi77(at)yandex(dot)ru>
To: Louis-David Mitterrand <vindex+lists-pgsql-sql(at)apartia(dot)org>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: "left join" not working?
Date: 2010-02-12 11:57:10
Message-ID: 23141265975830@webmail112.yandex.ru
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> where p.id_line=1

this filters rows after join was applied. Try this

select c.id_currency,max(p.modified_on) from currency c left join
price_line p using (id_currency) where (p.id_line=1 or p.id_line is null) group by
c.id_currency;

> Hi,
> This query:
> select c.id_currency,max(p.modified_on) from currency c left join
> price_line p using (id_currency) where p.id_line=1 group by
> c.id_currency;
> doesn't list all c.id_currency's, only those with a price_line. However
> this one does:
> select c.id_currency,max(p.modified_on) from currency c left join
> price_line p on (p.id_currency = c.id_currency and p.id_line=1) group by
> c.id_currency;
> How come?
> Thanks,
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