Message-ID: <427E892A.1000107@ontko.com>
Date: Sun, 08 May 2005 16:48:26 -0500
From: Nick Fankhauser <nickf@ontko.com>
Reply-To: nickf@doxpop.com
Organization: Ray Ontko & Co.
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To: Alvaro Herrera <alvherre@dcc.uchile.cl>
Cc: nickf@doxpop.com, pgsql-sql@postgresql.org
Subject: Re: interesting SQL puzzle - concatenating column with itself.
References: <427E60BC.8060701@ontko.com>
 <20050508212905.GA14422@dcc.uchile.cl>
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Excellent! Thanks for providing both the idea and an example. I didn't get the idea right away, but the example made it clear. I'll try that on my table and report back on how it works out.

Regards,
     -Nick


------------------------------------------------------------------
Nick Fankhauser    

   nickf@ontko.com   Phone 765.935.4283   Fax 765.962.9788
       Ray Ontko & Co. - Software Consulting Services
                     http://www.ontko.com
 

Alvaro Herrera wrote:

> 
> You can create a custom aggregate to do concatenation and group by
> memo_id.
> 
> create or replace function text_cat(text, text) returns text called on null input
> language sql immutable as 'select case when $1 is null then $2 when $2
> is null then $1 else $1 || '' '' || $2 end';
> 
> create aggregate textcat (basetype = text, sfunc = text_cat, stype = text);
> 
> create table memos (memo_id int, sequence int, memo_text text);
> insert into memos values (666, 3, 'jumped over');
> insert into memos values (666, 1, 'The quick');
> insert into memos values (666, 4, 'the lazy brown dog');
> insert into memos values (666, 2, 'red fox');
> 
> select memo_id, textcat(memo_text) from (select * from memos order by
> memo_id, sequence) as foo group by memo_id;
> 
> 
> The order is not really guaranteed, though if this is a one-shot thing,
> you may get away with turning off hashed aggregates.
>