From: Richard Huxton <dev@archonet.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: terry@ashtonwoodshomes.com, "Postgresql Sql Group (E-mail)" <pgsql-sql@postgresql.org>
Subject: Re: Return relation table data in a single value CSV
Date: Wed, 18 Feb 2004 09:29:42 +0000
Message-ID: <200402180929.42103.dev@archonet.com> (raw)
In-Reply-To: <18788.1077060834@sss.pgh.pa.us>
References: <007701c3f591$5acc3020$2766f30a@development.greatgulfhomes.com>
<200402172104.38307.dev@archonet.com>
<18788.1077060834@sss.pgh.pa.us>
On Tuesday 17 February 2004 23:33, Tom Lane wrote:
> Richard Huxton <dev@archonet.com> writes:
> > 2. Write a custom aggregate function (like sum()) to do the
> > concatenation. This is easy to do, but the order your ABC get processed
> > in is undefined.
>
> Actually, as of 7.4 it is possible to control the order of inputs to a
> custom aggregate. You do something like this:
>
> SELECT foo, myagg(bar) FROM
> (SELECT foo, bar FROM table ORDER BY foo, baz) AS ss
> GROUP BY foo
>
> The inner sub-select must order by the columns that the outer will group
> on; it can then order by additional columns that determine the sort
> order within each group. Here, myagg() will see its input ordered by
> increasing values of baz.
Hmm - good to know, but I'm always wary of doing this sort of thing. It's
exactly the sort of trick I look at 18 months later, fail to read my own
comments and "tidy" it.
--
Richard Huxton
Archonet Ltd
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To: pgsql-sql@postgresql.org
Cc: dev@archonet.com, tgl@sss.pgh.pa.us
Subject: Re: Return relation table data in a single value CSV
In-Reply-To: <200402180929.42103.dev@archonet.com>
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