Message-ID: <466670CF.8020303@archonet.com>
Date: Wed, 06 Jun 2007 09:31:11 +0100
From: Richard Huxton <dev@archonet.com>
User-Agent: Thunderbird 2.0.0.0 (X11/20070326)
MIME-Version: 1.0
To: Drew <drewmwilson@fastmail.fm>
Cc: pgsql-sql@postgresql.org
Subject: Re: How to find missing values across multiple OUTER JOINs
References: <4FD9368D-D4CA-44CF-887B-EBB64DCE46BA@fastmail.fm>
In-Reply-To: <4FD9368D-D4CA-44CF-887B-EBB64DCE46BA@fastmail.fm>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Drew wrote:

> This seems to me the appropriate situation for using OUTER JOINs, but I 
> cannot figure out how to get the null rows without the not-null rows.

> However, when I try to exclude the one not-null row, doing this:
>   SELECT 
> s.source_id,tp.translation_pair_id,t.translation_id,t.language_id, l.name
>     FROM (select * FROM source s WHERE source_id = 159986) AS s
>         LEFT OUTER JOIN translation_pair tp USING(source_id)
>         LEFT OUTER JOIN translation t ON tp.translation_id = 
> t.translation_id AND t.translation_id IS NULL
>         RIGHT OUTER JOIN language l on l.language_id = t.language_id;

Ah, you need to put the "IS NULL" outside the join.

SELECT
...
WHERE
   s.source_id IS NULL OR tp.translation_pair_id IS NULL OR ...
-- 
   Richard Huxton
   Archonet Ltd