merge result sets

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?

any hint is very much appreciated.

thanks
simon

--
Simon Litwan                               simon.litwan@wyona.com
Wyona Inc.  -   Open Source Content Management   -   Apache Lenya
http://www.wyona.com                      http://lenya.apache.org