Re: merge result sets

On Die, 2006-06-20 at 15:34 -0500, Bruno Wolff III wrote:
> On Tue, Jun 20, 2006 at 12:06:24 +0200,
> simon <simon(dot)litwan(at)wyona(dot)com> wrote:
> > hi all
> >
> > i'm using postgres 7.3
> >
> > my problem is i want to build a helper table:
> >
> > UPDATE studienmodul_summary
> > SET kategorie = (SELECT kategorie_bezeichnung
> >
> > if the SELECT gives back just one result row, everthing is easy. my
> > problem is, there is sometimes more than one result row.
> >
> > is there a way to concatenate all result rows and insert them in one
> > field?
>
> Yes. You can have the subselect call a custom aggregate function that does
> this for you. Sample code for doing this has been posted on the list
> multiple times and you should be able to find it in the archives.

thanks for this hint i didn't konw about the custom aggregate function.
i found comma_aggregate(text,text) amd similar examples.
unfortunatly i didn't found something like comma_aggregate(SELECT...).

is it possible to write an aggregate function that takes the result rows
of any number and makes a long string out of it?

it would be great if someone would have done something before and is
willing to share.
but hints where to find docu and/or howtos about writting
customaggregate functions are also very welcom.

simon
>
--
Simon Litwan simon(dot)litwan(at)wyona(dot)com
Wyona Inc. - Open Source Content Management - Apache Lenya
http://www.wyona.com http://lenya.apache.org