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Re: unique primary key shared between multiple tables.

From: Bob Badour <bbadour_at_golden.net>
Date: Mon, 17 Mar 2003 12:19:41 -0500
Message-ID: <AXnda.63$9r4.6831257@mantis.golden.net>


"programmer" <BROWNHIK_at_Syntegra.Bt.Co.Uk> wrote in message news:b549nv$a4p$1_at_pheidippides.axion.bt.co.uk...
> > > Put all private owners and business owners in the same table,
> > distinguished
> > > by a flag.
> >
> > From the original description of the problem, what makes you assume
> > PrivateOwner and BusinessOwner share any similar attributes other than
> > ownerNo?
> >
> Not very likely that they don't, is it?

Maybe a couple--I would not assume or speculate either way. What do you do with any attributes they do not share? The flag solution assumes they have the same attributes.

Why on earth would anyone want to mix two clearly different entity types in the same relation?

If yet another relation has a foreign key reference to BusinessOwner, your choices become: 1. Do not declare or enforce the integrity constraint or 2. Use much more complex and unwieldy constraint declarations.

> > What happens later when the business needs to introduce a
> > PublicSectorOwner?
> >
> Replace the flag with a character variable if there is any possibility
that
> this may be needed in the future.

How does one predict future possibility? Isn't anything possible?

And what is this about a "variable" ? A variable what? Received on Mon Mar 17 2003 - 11:19:41 CST

Original text of this message

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