Re: foreign key problem

----- Original Message -----
From: "ivan marchesini" <marchesini(at)unipg(dot)it>
To: <pgsql-sql(at)postgresql(dot)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