Re: 2nd Normal Form Question

On 8 feb, 17:21, gamehack <gameh..._at_gmail.com> wrote:
> Hi all,
>
> I'm currently evaluating whether a relation is in 2NF. The relation is
> defined as follows:
> <Year | Winner Name | Winner Votes | Party | Home State> in the
> context of an election. I've given a sample relation below.
> 1946 | MyName | 453 | MyParty | California
> The primary key for this relation is 'Year'.
>
> Now the question is whether this relation is in 2NF? What confuses me
> is that some books say the following:
> "Note that when a 1NF table has no composite candidate keys (candidate
> keys consisting of more than one attribute), the table is
> automatically in 2NF."
>
> Now, let's evaluate the functional dependencies for this relation.
> Year -> Winner Name
> Year -> Winner Votes
> Winner Name -> Party
> Winner Name -> Home State
>
> The definition for 2NF is as follows: "A 1NF table is in 2NF if and
> only if, given any candidate key and any attribute that is not a
> constituent of a candidate key, the non-key attribute depends upon the
> whole of the candidate key rather than just a part of it." (Wikipedia)
> which is consistent with the books I'm reading on databases.
>
> Now as this relation doesn't have a composite primary key, it follows
> that it is automatically in 2NF.

A small note here: you should check if there is a composite *candidate* key. It is in principle possible that the candidate key you picked as primary keys is not composite while at the same time there is another candidate that *is* composite, in which case the relation could very well not be in 2NF.

> But as we can see two non-prime
> attributes (party & home state) are functionally dependent only a
> subset of the primary key (the subset being the empty set). This must
> imply that it is not in 2NF.

They are not dependent on the empty set, but on the set {"Winner Name"}, which is clearly not a proper subset of a candidate key. So no 2NF violation there.

• Jan Hidders