Re: One-To-One Relationships

From: David Cressey <>
Date: Tue, 30 Oct 2007 19:57:39 GMT
Message-ID: <T0MVi.1168$pT.133_at_trndny07>

"paul c" <> wrote in message news:0aIVi.160673$1y4.23786_at_pd7urf2no...
> David Cressey wrote:
> > "Phil Reynolds" <> wrote in message
> > news:CGzVi.2012$
> >> One thing that's not clear to me is when it's appropriate to create a
> >> one-to-one relationship. I mean, in some cases it's obvious, if there's
> >> set of data that wouldn't always apply; then you'd want to create that
> >> of fields in a separate table with a one-to-one relationship. But in
> >> other cases? After the number of fields in a table is greater than X?
> >>
> >> I'm just curious about what thoughts/theories/ideas people have about
> >> one-to-one relationships, because that's something that's never been
> >> entirely clear to me.
> >>
> >
> > I think that a relationship is something you discover, not something you
> > create. Are you talking about creating two tables where there is a
> > one-to-one relationship between rows in table A and rows in table B?
> > so, I think what you have created is not the relationship as such, but
> > way of representing it in the database.
> >
> > I hope this isn't too nit picky. I think the distinction between what
> > discover via analysis and what you create during implementation
> > design) is very fundamental, and needs to be kept clear in all our
> > discussions.
> >
> >
> >


> I don't think it's too nit picky at all. I wish the OP had given an
> example because I think people here are talking about two different
> things as you suggest, ie., a one-to-one as the ER people would see it
> (eg., dept has one mgr and mgr has one dept) versus a relation that
> somebody wants to make into two relations.


It gets even foggier because many of us (myself included) use the term "relation" in reference to something that, in the strictest mathematical definition, is really a "relationship". Received on Tue Oct 30 2007 - 20:57:39 CET

Original text of this message