Re: What are the differences between the terms, CANDIDATE KEY, PRIMARY KEY, SUPER KEY, COMPOSITE KEY?

Now that I have understood the different types of keys and their differences, can you tell me what is a NON-PRIME ATTRIBUTE? Is it an attribute which is not a candidate key?
Brian Selzer wrote:
> A superkey is a set of attributes which uniquely identifies a tuple in a
> relation.
>
> A candidate key is an irreducible set of attributes which uniquely
> identifies a tuple in a relation.
>
> A composite key is a candidate key that has more than one attribute.
>
> The primary key is a candidate key. Any candidate key can be the primary
> key, but usually the candidate key that participates in referential
> constraints is designated as the primary key.
>
> (a) is imprecise. A collection is different from a set: it's a multiset.
> Also, a candidate key must be irreducible, meaning that if any of the
> attributes are excluded, the remaining attributes do not uniquely identify a
> tuple.
>
> (b) is incorrect. The database designer, not the DBMS, chooses which
> candidate key is primary. In addition, a candidate key can have more than
> one attribute, so it's possible to have a composite primary key.
>
> I've addressed (c) above.
>
> A candidate key is a superkey, but a superkey is not necessarily a candidate
> key. A superkey may be reducible, meaning that even if one or more
> attributes are excluded, the remaining attributes still uniquely identify a
> tuple.
>
> "Abhishek" <abhisheksgumadi_at_gmail.com> wrote in message
> news:1140522359.762187.213930_at_o13g2000cwo.googlegroups.com...
> > Hi,
> > Can anybody tell me the differences between the above mentioned terms?
> > Also please tell me if one can be the other and vice versa..please
> > elaborate with the helpof a table if possible. Also please tellme if
> > the below statement by me is correct..
> > a) Any attribute or a collection of attributes which uniquely
> > identifies the tuples in a relation is called a canditate key.this
> > candidate key thus can contain a single attribute or a collection of
> > attributes.
> > b) one of the attributes is chosen by the DBMS to identify the tuples
> > uniquely and this attribute is called the primary key.
> > c) A primarykey is a candidate key.all candidate keys cannot be a
> > primary key.
> > Now,,,what is the superkey?
> >
Received on Fri Feb 24 2006 - 18:56:09 CET