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To: Martin Marques <martin@bugs.unl.edu.ar>
Cc: pgsql-sql@postgresql.org
Subject: Re: select by groups
References: <200403011920.20505.martin@bugs.unl.edu.ar>
In-Reply-To: <200403011920.20505.martin@bugs.unl.edu.ar>
From: Manuel Sugawara <masm@fciencias.unam.mx>
User-Name: Manuel Sugawara
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Date: 01 Mar 2004 16:32:50 -0600
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Martin Marques <martin@bugs.unl.edu.ar> writes:

> I have a table with names of people, email address, etc, and an identifier 
> that tells me which group they are in (could be a 1, 2, or 3 person group). 
> Is it posible to make a query that would give me the name of the persons of 
> each group in one row? Or do I have to do PL?

Use GROUP BY with an aggregator that concatenate the names. The
aggregator may be implemented in plpgsql, for instance:

CREATE OR REPLACE FUNCTION concat (text, text) RETURNS text
    AS 'select case when $1 = '''' then $2 else ($1 || '', '' || $2) end'
    LANGUAGE sql;
 
CREATE AGGREGATE concat (
    BASETYPE = text,
    SFUNC = public.concat,
    STYPE = text,
    INITCOND = ''
);

Regards,
Manuel.