views and null bothering

I have a bunch of tables which I give access through a view. The problem is
that in the main table there are columns, that are referenced to another
tables column, that have NULLs.
In the SELECT inside the view's definition I put the join equality, but have
lots of trouble makeing it put correctly the columns that have NULL values.

This is what I tried:

CREATE VIEW admin_view
SELECT id_curso,car.carrera,titulo,
car.categoria AS car_categ,
categ.categoria, categ.descripcion AS categ_desc
FROM carrera car,resol,inscripcion ins,niveles niv, categ
WHERE resol.carr=car.id_curso AND niv.id_nivel=car.nivel
AND area.id_subarea=car.area AND ins.carrera=car.id_curso
AND categ.id_categ=car.categoria;

But this one doesn't show rows with NULL on column car.categoria.

CREATE VIEW admin_view
SELECT id_curso,car.carrera,titulo,
car.categoria AS car_categ,
categ.categoria, categ.descripcion AS categ_desc
FROM carrera car,resol,inscripcion ins,niveles niv, categ
WHERE resol.carr=car.id_curso AND niv.id_nivel=car.nivel
AND area.id_subarea=car.area AND ins.carrera=car.id_curso
AND (categ.id_categ=car.categoria OR car.categoria IS NULL);

This one repeats rows with NULLs on column car.categoria, one repeate for
each row element in the categ table, which is not what I need.

The last thing I thought about, but am not sure if it's exactly what I want
(may do things I doen't want with some queries), is to put a DISTINCT ON
(id_curso), which would be a solution for the multiple row problem, but I
would need to add a CASE in the categ.categoria, so that it gives me NULL
when car.categoria ISNULL.

Am I complicating it to much? Is there an easier way out?

Saludos... :-)

--
Cualquiera administra un NT.
Ese es el problema, que cualquiera administre.
-----------------------------------------------------------------
Martin Marques | mmarques(at)unl(dot)edu(dot)ar
Programador, Administrador | Centro de Telematica
Universidad Nacional
del Litoral
-----------------------------------------------------------------