Re: How to find missing values across multiple OUTER JOINs

On þri, 2007-06-05 at 23:55 -0700, Drew wrote:
> I'm having troubles using multiple OUTER JOINs, which I think I want
> to use to solve my problem.
>
> My problem is to find all non-translated string values in our
> translations database, given the 4 following tables:
>
> SOURCE (source_id PRIMARY KEY, language_id, value, ...)
> TRANSLATION (translation_id PRIMARY KEY, language_id, value, ...)
> TRANSLATION_PAIR (source_id, translation_id)
> LANGUAGE(language_id PRIMARY KEY, name)
>
> 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.
>
> Here's my best guess at this query:
> SELECT
> s.source_id,tp.translation_pair_id,t.translation_id,t.language_id,
> l.name
>
> FROM source 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
move this condition out of the ON clause into a WHERE clause
> )
> RIGHT OUTER JOIN language l on l.language_id = t.language_id;

SELECT s.source_id,
tp.translation_pair_id,
t.translation_id,
t.language_id,
l.name
FROM source s
LEFT OUTER JOIN translation_pair tp USING(source_id)
LEFT OUTER JOIN translation t ON tp.translation_id = t.translation_id
RIGHT OUTER JOIN language l
on l.language_id =t.language_id
WHERE t.translation_id is null;

(i did not check the rest of your query)

hope this helps,
gnari