Yes, because your WHERE is something that comes after the operation
of the LEFT JOIN, in practice, defeating the purpose you intented.
On your second query the p.id_line = 1 doesn't do that because it is part of
the LEFT JOIN itself..
HTH
Best,
Oliveiros d'Azevedo Cristina
----- Original Message -----
From: "Louis-David Mitterrand" <vindex+lists-pgsql-sql@apartia.org>
To: <pgsql-sql@postgresql.org>
Sent: Friday, February 12, 2010 11:57 AM
Subject: Re: [SQL] "left join" not working?
> On Fri, Feb 12, 2010 at 11:35:02AM -0000, Oliveiros C, wrote:
>> 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...
>
> So, if I understand correctly, a WHERE filters all results regardless of
> join conditions and can turn an OUTER JOIN into an INNER JOIN.
>
> Thanks for pointing that out!
>
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