select distinct and order by

Hello everybody,

I have a short question:

I'm trying to run the following query:
select distinct on (staff_id) staff_id, fullname, loginname from staff
where staff_id in  (select staff_id from staffmembership where staffgroup_id=#SomeIdValue#)
order by fullname

I get the follwing error:
select distinct on expressions must match the initial order by expression

Does this mean that I can only order by the same fields as the ones that I use in the distinct?
If so, is there still a way that I can select distinct on the keyfield, and still sort by the name. However unlikely,
itcould happen that two people have the same name, so a distinct on fullname could make problems. 

The facts:
- PostgreSQL 7.3.2 running on RH 9
- pgODBC 7.3.0200
- Borland Delphi 7 enterprise

Regards,

Stijn Vanroye

-=[Today I got more responsabilities from my boss, as from now I'm responsible for everything that goes wrong ...]=-