Message-ID: <723CFC801B0846B9B31DCE45B62222FA@marktestcr.marktest.pt>
From: "Oliveiros C," <oliveiros.cristina@marktest.pt>
To: "Louis-David Mitterrand" <vindex+lists-pgsql-sql@apartia.org>,
	<pgsql-sql@postgresql.org>
References: <20100212111453.GA16318@apartia.fr>
	<34E07A4C4CDA4FFCB56CD63C675568ED@marktestcr.marktest.pt>
	<20100212115747.GA21659@apartia.fr>
Subject: Re: "left join" not working?
Date: Fri, 12 Feb 2010 12:17:35 -0000
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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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