doing VALID UNTIL programmatically in SQL ?

Hi all,

in a psql script for GnuMed (www.gnumed.org) I am using a
snippet like the following for setting up predefined test
accounts:

CREATE USER "test-doc"
    WITH PASSWORD 'test-doc'
    IN GROUP "gm-doctors", "gm-public"
    VALID UNTIL '2003-09-30'
;

I would like to constrain their validity to, say, six months. I
have tried but not found a way to tell the VALID UNTIL clause
something like

    now() + '6 months'::interval

Anyone have a suggestion (short of calculating in the client at
runtime and substituting) on how to do this in plain SQL ?

Thanks a lot,

Karsten Hilbert, MD
GnuMed i18n coordinator
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