Re: null as part of key?

yes. i get it now. thanks for the help.

i need a sequence as a pk with a non uniuque index.

"Howard J. Rogers" <howardjr_at_www.com> wrote in message news:3bd5e923$0$9822$afc38c87_at_news.optusnet.com.au...
> It's not "OK" for a unique index: the index won't contain pointers to
table
> records that have a null value in the key field. So it's not really
> 'ok' -we just ignore them. It is OK for a unique *constraint*, because
> uniqueness simply means not having a value another record has. Since null
> means 'unknown', we can't compare null with null, and hence records with
> null values in the constrained column can't possibly be duplicating each
> other -we simply don't know what their value is.
>
> But a primary key is used to identify, uniquely, *every* row in a table,
> with no skipping of awkward rows, and I don't rate your chances of ever
> identifying anything if you don't know what it is that you're looking for!
>
> Regards
> HJR
> --
>
> Oracle Resources : http://www.geocities.com/howardjr2000
> ========================================
>
>
> "ed zappulla" <zappullae_at_rcn.com> wrote in message
> news:9r42ov$k4m$1_at_bob.news.rcn.net...
> > i agree that a non business id would work.
> >
> > i don't understand why null is not a valid value for a key part but is
ok
> > for a unquie index.
> >
> >
> > "Henning Follmann" <h.follmann_at_gmx.de> wrote in message
> > news:slrn9tamm8.hl.h.follmann_at_mobile.follmann-net...
> > > On Mon, 22 Oct 2001 11:40:57 -0400, ed zappulla <zappullae_at_rcn.com>
> wrote:
> > > > I see. What about this case
> > > >
> > > > country
> > > > state
> > > > city
> > > > some other cols
> > > >
> > > > pk = country, state, city
> > > >
> > > > Some contries don't have states; therefore it would be null for
those
> > > > countries.
> > > >
> > >
> > > The problems you are just encountering show some flaws in your
> > > datamodeling.
> > >
> > > 1) do not use production data as a primary key
> > >
> > > This is a good rule!
> > >
> > > Suggestion:
> > >
> > > Create a metadata table:
> > > it includes for every country the meta information about address
> formats.
> > > Use for the countries the iso standard! Sooner or later you will be
> > > thankfull you did so!
> > >
> > > now the rough design
> > >
> > > Party : Party_ID, PartyType_ID
> > >
> > > Address: Party_ID, AddressMeta_ID, ...
> > >
> > > AddressMeta: AddressMeta_ID, Country_ID, Field1, Field1Flag (Mand,
Opt,
> > > notuse) ...
> > >
> > > Country: Country_ID (Num(3)), Name, A2, A3
> > >
> > >
> > >
> > >
> > > I use also Party, because you might have Companies, private Persons
...
> > > A Party might have also more than one Address, so you might tweak it
for
> > > your purposes.
> > > It might also a good idea to place some rules for checking the data
> > > depending on the country. If you use MetaData this gives you the
> > > flexibility to stor the validation rules (names of procedures) in your
> > > table.
> > >
> > >
> > > Good luck,
> > > dealing with international addresses, currencies, etc. is not easy.
> > > I hope this helps.
> > >
> > >
> > >
> > >
> > > > does this make sense?
> > > >
> > > >
> > > >
> > > > "Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in
> > message
> > > > news:3bd42f49$0$237$ed9e5944_at_reading.news.pipex.net...
> > > >> No. Nor in any version. If you think carefully you will see that
> > allowing
> > > >> this would be a nonsense.
> > > >>
> > > >>
> > > Cheers,
> > > henning
> > >
> > > --
> > > Henning Follmann | 8 Jane Road
> > > Tel.: +1 908 656 7061 | New Providence, NJ 07974
> > > H.Follmann_at_gmx.de | USA
> > >
> > >
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>
Received on Thu Oct 25 2001 - 11:50:21 CDT