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.
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Martin Marques                  |        mmarques@unl.edu.ar
Programador, Administrador      |       Centro de Telematica                      Universidad Nacional
        del Litoral
 
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