From: Dawid Kuroczko <qnex42@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Re: Columns into rows.
Date: Thu, 13 Jan 2005 11:45:52 +0100
Message-ID: <758d5e7f0501130245e2e6fb1@mail.gmail.com> (raw)
In-Reply-To: <758d5e7f05011302265be7e12a@mail.gmail.com>
References: <758d5e7f05011302265be7e12a@mail.gmail.com>
On Thu, 13 Jan 2005 11:26:04 +0100, Dawid Kuroczko <qnex42@gmail.com> wrote:
> I can write:
>
> SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE id
> = <<NUM>> AND pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id,
> path AS path_bb FROM new_table_paths WHERE id = <<NUM>> AND pathtype =
> 'bb') AS bb; [ and so on... ]
>
> And its fast; however if I move WHERE id = <<NUM>> outside selects
> (for views), it first "materializes" old layout, and then selects
> id... total waste.
>
> SELECT * FROM (SELECT id, path AS path_a FROM new_table_paths WHERE
> pathtype = 'a') AS a NATURAL FULL OUTER JOIN (SELECT id, path AS
> path_bb FROM new_table_paths WHERE pathtype = 'bb') AS bb WHERE id =
> <<NUM>>;
>
> I wonder if you know other way to write this join so it has good performace?
> Once again, I need a SELECT since I want a VIEW. :-)
Hmm, something like a multiple column returning aggregate...
As far as I know it is not possible to create aggregate which
could return more than one column? I'm thinking about
something like this:
SELECT id,r2c_aggregate(pathtype, path) FROM new_table_paths GROUP BY id;
...where r2c_aggregate(..) would be a plpgsql function doing the
pathtype+path --> path_a = path, path_bb = path2, path_ccc = path3
assembly. And it would be quite efficient I guess! :)
Hmm, r2c_aggregate could return array of arrays of pathtype/path pairs,
which could be processed by other function which would convert them
into rows, but this is UGLY(TM). :)
Regards,
Dawid
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Subject: Re: Columns into rows.
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