Thread: foreign key problem

Dear users,
I'm trying to create constraints into a db they give me from access...
I'm using pgadmin to create a new foreign key for the relationship
between two table..

I have a table called "generalita" wich contains a column called
"cod_carg":
___________________
select cod_carg from generalita group by cod_carg;cod_carg
----------
201
(4 righe)
___________________


I have another table, called "diz_carg" that contain, into a column
called "cod_carg" (that is a primary key), the domain values for the
"cod_carg" column of "generalita":
__________________
select cod_carg from diz_carg group by cod_carg;cod_carg
----------102
(3 righe)
__________________



so when I try to create the foreign key I obtain:
ALTER TABLE generalita ADD CONSTRAINT fkey_diz_cod_carg FOREIGN KEY
(cod_carg) REFERENCES diz_carg (cod_carg) ON UPDATE NO ACTION ON DELETE
NO ACTION;

____________________________
ERROR:  insert or update on table "generalita" violates foreign key
constraint "fkey_diz_cod_carg"
DETAIL:  Key (cod_carg)=(  ) is not present in table "diz_carg".
____________________________


can I allow null values for "generalita.cod_carg" although it is a
foreign key for "diz_carg.cod_carg"?

I apologize if it is a stupid question....   :-(

many thanks to all




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Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a 
06125
Perugia (Italy)
e-mail: marchesini@unipg.it       ivan.marchesini@gmail.com
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----- Original Message ----- 
From: "ivan marchesini" <marchesini@unipg.it>
To: <pgsql-sql@postgresql.org>
Sent: Monday, September 24, 2007 6:04 PM
Subject: [SQL] foreign key problem


> Dear users,
> I'm trying to create constraints into a db they give me from access...
> I'm using pgadmin to create a new foreign key for the relationship
> between two table..
>
> I have a table called "generalita" wich contains a column called
> "cod_carg":
> ___________________
> select cod_carg from generalita group by cod_carg;
> cod_carg
> ----------
>
> 2
> 0
> 1
> (4 righe)
> ___________________
>
>
> I have another table, called "diz_carg" that contain, into a column
> called "cod_carg" (that is a primary key), the domain values for the
> "cod_carg" column of "generalita":
> __________________
> select cod_carg from diz_carg group by cod_carg;
> cod_carg
> ----------
> 1
> 0
> 2
> (3 righe)
> __________________
>
>
>
> so when I try to create the foreign key I obtain:
> ALTER TABLE generalita ADD CONSTRAINT fkey_diz_cod_carg FOREIGN KEY
> (cod_carg) REFERENCES diz_carg (cod_carg) ON UPDATE NO ACTION ON DELETE
> NO ACTION;
>
> ____________________________
> ERROR:  insert or update on table "generalita" violates foreign key
> constraint "fkey_diz_cod_carg"
> DETAIL:  Key (cod_carg)=(  ) is not present in table "diz_carg".
> ____________________________
>
>
> can I allow null values for "generalita.cod_carg" although it is a
> foreign key for "diz_carg.cod_carg"?
>
> I apologize if it is a stupid question....   :-(
>
> many thanks to all
>
>


Yes you can , check that column cod_carg of table generalita is not set to 
NOT NULL.

With regards Ashish