Re: Differentiate between candidate key and super key

From: Bernhard Nemec <nemec_at_mem.unibe.ch>
Date: 2000/03/07
Message-ID: <38C4C9E5.89EF3074_at_mem.unibe.ch>#1/1


Joe \"Nuke Me Xemu\" Foster wrote:
>
> "Low Yew Sing" <slasher_at_singnet.com.sg> wrote in message news:89m0im$hu7$1_at_violet.singnet.com.sg...
>
> > How to differentiate between a candidate key and a super key? i can;t
> > understand what my txtbk is trying to say? Anybody can help?
> > If possible, quote examples.
>
> Doesn't a superkey have unnecessary junk in addition to what's needed to
> uniquely identify a record? If a person can be uniquely identified by
> either the full name or a taxpayer ID number, both are candidate keys.
> Combining the name and, say, the gender would be a superkey, since the
> person can be identified by the name alone.
>

A candidate key is always also a superkey. But a superkey _may_ contain additional fields that are not actually needed, while a candidate key is always minimal.

Bernhard Received on Tue Mar 07 2000 - 00:00:00 CET

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