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(at)mat(dot)cc>
To: pgsql-sql(at)postgresql(dot)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(at)mat(dot)cc, mat(at)absolight(dot)fr
isa | isa(at)mat(dot)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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