Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 01 Nov 2006 13:07:54 GMT
Message-ID: <K_02h.13017$cz.216303_at_ursa-nb00s0.nbnet.nb.ca>
>
> It's either {ABC} or {D} where D is an artificial identifier (e.g. a
> sequence number).
Date: Wed, 01 Nov 2006 13:07:54 GMT
Message-ID: <K_02h.13017$cz.216303_at_ursa-nb00s0.nbnet.nb.ca>
Godspeed wrote:
> <saturnlee_at_yahoo.com> wrote in message
> news:1162158876.794350.29460_at_f16g2000cwb.googlegroups.com...
>
>>I have a basic question. >>Suppose there are 3 attributes: A,B and C. >>And there are no FD(trivial and non trivial ) >> >>What 's the key for it? ABC or nothing???
>
> It's either {ABC} or {D} where D is an artificial identifier (e.g. a
> sequence number).
The introduction of an additional attribute has no effect whatsoever on the keys of the existing relation. All you have done is introduce functional dependencies: D <-> ABC Received on Wed Nov 01 2006 - 14:07:54 CET