Union instead of Outer Join

Hi,

I have this query in oracle which I'am trying to port to PostgreSQL :

Select
item_code, nvl(user_id,' ') as user_id
from
item_list L, User_detail B, User_detail S
where
L.user_id = S.User_id and
L.other_userid = B.user_id(+) and
L.item_code = 1234;

This query gives me 1 row as result. L.other_userid could be null.

I try changing the query thus in postgreSQL :

Select
item_code, nvl(user_id,' ') as user_id
from
item_list L, User_detail B, User_detail S
where
L.user_id = S.User_id and
L.other_userid = B.user_id and
L.item_code = 1234
Union
Select
item_code, nvl(user_id,' ') as user_id
from
item_list L, User_detail B, User_detail S
where
L.user_id = S.User_id and
L.item_code = 1234 and
0 = ( Select
count(*)
from
listed_items L, user_detail B, user_detail S
where
L.other_userid = B.user_id);

The above query does not return any row. Where could I be going wrong?

Any help would be appreciated.

Thanx in advance

Unni