Help with UNION query

Hi all, I have the followin query:

SELECT g.id
from onp_group g
where g.groupname IN
(SELECT ug.groupname from onp_user_group ug WHERE ug.username = 'andreak')
UNION (SELECT child_id
FROM onp_group_children
WHERE group_id IN
(SELECT g.id from onp_group g
where g.groupname IN (SELECT ug.groupname from onp_user_group ug WHERE
ug.username = 'andreak')));

Any ideas on how I can simplyfy this query so that I only need to provide
ug.username='andreak' once? I would much rather prefer a query which doesn't
involve UNION or SUB-SELECTS.

Here are the table-definitions:

CREATE TABLE onp_group(
id integer PRIMARY KEY REFERENCES onp_entity(id) on delete cascade,
p_id integer REFERENCES onp_group(id) on delete cascade,
groupname varchar NOT NULL unique
);

CREATE TABLE onp_group_children(
group_id integer NOT NULL REFERENCES onp_group(id),
child_id integer NOT NULL REFERENCES onp_group(id),
UNIQUE(group_id, child_id)
);

CREATE TABLE onp_user_group(
groupname varchar not null REFERENCES onp_group(groupname) ON DELETE CASCADE
ON UPDATE CASCADE,
username varchar not null REFERENCES onp_user(username) ON DELETE CASCADE ON
UPDATE CASCADE,
primary key(groupname, username)
);

--
Andreas Joseph Krogh <andreak(at)officenet(dot)no>
Senior Software Developer / Manager
gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
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