pg_user, changing priviliges

I'm trying to give a createuser privilige by changing pg_users, i'm logged
in as a superuser.

mtldb=# select count(*) from pg_user  where usename='mtluser';
 count
-------
     1
(1 row)

mtldb=# update pg_user set usesuper=true, usecatupd=true where
usename='mtluser';
UPDATE 0

Why I can't do it?

tia


Marcin Mazurek

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Kierownik Działu Systemowego
MULTINET SA o/Poznan
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