My first guess is that
NULL fails the condition on your WHERE clause,
p.id_line = 1
So your WHERE clause introduces an additional level of filtering that
filters out the NULLs coming from the LEFT JOIN...
Didn't do any tests, it's just a guess...
Best,
Oliveiros
----- Original Message -----
From: "Louis-David Mitterrand" <vindex+lists-pgsql-sql@apartia.org>
To: <pgsql-sql@postgresql.org>
Sent: Friday, February 12, 2010 11:14 AM
Subject: [SQL] "left join" not working?
> 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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