Re: How do I concatenate row-wise instead of column-wise?

Hi Marcus,

It is simple ,

you need to write a function  and define an aggregate using that function.

in case you have already searched for
the solution and not found here  it is from this mailing list only:

===========================================================================
Date: Tue, 14 May 2002 18:13:09 +0200
From: Mathieu Arnold <mat@mat.cc>
To: pgsql-sql@postgresql.org
Subject: [SQL] aggregate...
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Hi

I have this :

CREATE FUNCTION "comma_cat" (text,text) RETURNS text AS '
SELECT CASE WHEN $2 IS NULL OR $2 = '''' THEN $1           WHEN $1 IS NULL OR $1 = '''' THEN $2           ELSE $1 ||
'','' || $2      END 
' LANGUAGE 'sql';


CREATE AGGREGATE list ( BASETYPE = text, SFUNC = comma_cat, STYPE = text,
INITCOND = '' );

I can use it as :
select user, list(email) from user join email using (id_user);

user   | list
-------+-----------------------------
mat    | mat@mat.cc, mat@absolight.fr
isa    | isa@mat.cc

===============================================================

regds

On Tuesday 16 July 2002 13:39, you wrote:
> I have a table like this:
> SELECT * FROM old_tab;
> id    |    descr
> -------------------
> 1    |    aaa
> 1    |    aaa
> 1    |    bbb
> 2    |    ccc
> 2    |    bbb
> 3    |    ddd
> 3    |    ddd
> 3    |    eee
> 3    |    fff
> 4    |    bbb
> etc...
>
> And I want a new table where the descr is concatenated row-wise like this:
> SELECT * FROM new_tab;
> id    |    descr
> --------------------------
> 1    |    aaa;bbb
> 2    |    ccc;bbb
> 3    |    ddd;eee;fff
> 4    |    bbb
> etc...
>
> This is the closest I get....:
> UPDATE new_tab SET descr = old_tab.descr||' ; '||old_tab.descr from
> old_tab where old_tab.id=new_tab.id;
> UPDATE 4
> SELECT * FROM new_tab ;
>  id |   descr
> ----+-----------
>  1  | aaa ; aaa
>  2  | ccc ; ccc
>  3  | ddd ; ddd
>  4  | bbb ; bbb
> etc...
>
> Thus, the concatenating operator never works on other rows than the
> present. How can I get around that and still stick to the postgresql
> syntax?
>
> Regards
> Marcus
>
>
>
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