Re: Primary -- foreign keys

I tried that on DB2...same behavior.
-Aakash

"volo" <yariv_volovelsky_at_yahoo.com> wrote in message news:3b74700d$0$1087$9b622d9e_at_news.freenet.de...
>
> "Pavol Obecajcik" <Pavol.Obecajcik_at_onatix.com> wrote in message
> news:f19254f5.0108101207.6c3e4535_at_posting.google.com...
> > prk25_at_yahoo.com (keith) wrote in message
> news:<adbca63f.0108100550.b176fc5_at_posting.google.com>...
>
> ...
> > > create table abc
> > > (
> > > x integer primary key,
> > > y char(20),
> > > foreign key (x) references abc(x)
> > > );
> > >
> > > What's being accomplished by creating a forein key which references a
> > > primary key of the same table??? Primary and foreign keys are on the
> > > same column of the same table????
> > >
> > > Thanks
> > >
> > > Keith
> >
> >
> > Hi,
> > This is nonsense :-).
> >
> > Primary key is (must be) UNIQUE and NOT NULL.
> >
> > 1. Foreign key must hold only existing values from referenced column
> > (eventually NULL) => violated unique restriction.
> > 2. NOT NULL restriction => impossible to insert first row in table
> >
> > try this:
> > create table abc
> > (
> > x integer not null primary key,
> > parent_abc integer,
> > y char(20)
> > )
> > ;
> > alter table abc add foreign key (parent_abc) references abc(x)
> > ;
> >
> > Palo
>
> Hi,
>
> I also thought it was nonsense :-) and came theoretically to the same
> conclusion that you can't insert the first row.
> Then I tried it with personal Oracle and I was ABLE to insert some rows.
> So I suppose Oracle is right and we're are wrong. :-(
>
> can someone explain the meaning of this?
>
> Yariv
>
>
>
>
Received on Tue Aug 14 2001 - 01:00:42 CEST