Обсуждение: 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@unl.edu.ar
Programador, Administrador | Centro de Telematica Universidad Nacional
del Litoral
-----------------------------------------------------------------
Martin, > 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. You need to use LEFT OUTER JOIN, supported in Postgres 7.1.x. See the current postgresql docs, or your favorite ANSI-SQL handbook, for guidance. -Josh Berkus ______AGLIO DATABASE SOLUTIONS___________________________ Josh Berkus Complete informationtechnology josh@agliodbs.com and data management solutions (415) 565-7293 for law firms, small businesses fax 621-2533 and non-profit organizations. San Francisco
On Lun 06 Ago 2001 21:02, Josh Berkus wrote:
> Martin,
>
> > 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.
>
> You need to use LEFT OUTER JOIN, supported in Postgres 7.1.x.
>
> See the current postgresql docs, or your favorite ANSI-SQL handbook, for
> guidance.
Sorry for the late answer, but... THANKS ALOT! It's the first time I use
OUTER JOINS, and I think they are great! Thanks Tom for this great feature.
Saludos... :-)
--
Cualquiera administra un NT.
Ese es el problema, que cualquiera administre.
-----------------------------------------------------------------
Martin Marques | mmarques@unl.edu.ar
Programador, Administrador | Centro de Telematica Universidad Nacional
del Litoral
-----------------------------------------------------------------