Sorry about the brackets I guess it's Oracle's way of saying that it makes no sense.

I don't have time to build a realistic example - but if you can imagine the following to use four different tables it should give you a start (this time I checked it! - 8.1.7) you would probably need to replace the "select *" with column names:
Code:
select * from
rl_admin_flags a, rl_configuration b
where a.rlparameter = b.rlparameter
   UNION ALL
select * from
rl_admin_flags c, rl_configuration d
where c.rlparameter = d.rlparameter
and   not exists
(select * from rl_configuration x
 where x.rlparameter = d.rlparameter)
Alternativly create two views to "encapsulate" your combination of tables.