Date: Thu, 21 Jun 2007 15:24:40 +0200
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-novice@postgresql.org, pgsql-sql@postgresql.org
Subject: Re: [SQL] Select last there dates
Message-ID: <20070621132440.GM1405@a-kretschmer.de>
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	<20070621095025.GG1405@a-kretschmer.de>
	<1c23c8e70706210600he74293ci83bdbc557ee2dba8@mail.gmail.com>
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am  Thu, dem 21.06.2007, um 16:00:05 +0300 mailte Loredana Curugiu folgendes:
> So Andreas, would you please give some more explanations
> on your solution? I didn't work with functions and aggregate till
> now.

I will try it, but i'm not a nativ english speaker and thats why i have
some problems...

> 
> I don't understand how this comma_aggregate works. I can see that this
> function it is defined with two arguments, but the aggredate it is called
> with a single argument.

An aggregate needs among others a so called 'SFUNC' with 2 parameters:
internal-state and next data item. It returns the next-internal-state.

This is explained here:
http://www.postgresql.org/docs/8.1/interactive/sql-createaggregate.html

> 
> And what is LANGUAGE sql IMMUTABLE STRICT ?

An IMMUTABLE function can't modify the database
http://www.postgresql.org/docs/current/static/xfunc-volatility.html


STRICT:
http://www.postgresql.org/docs/8.2/static/xfunc-c.html

,----[  ]
| Notice that we have specified the functions as "strict", meaning that
| the system should automatically assume a null result if any input value
| is null.
`----


Andreas
-- 
Andreas Kretschmer
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