Re: Advanced SQL

On 7 sep, 15:43, Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
> Quoth Evan Keel:
>
> > "David Portas" <REMOVE_BEFORE_REPLYING_dpor..._at_acm.org> wrote in message
> >news:pZSdnfih_oRy5H3bRVnyigA_at_giganews.com...
> >> Call me picky but I am not entirely comfortable with that U.Texas site,
> >> even though it's a commendable effort overall.
>
> >> "The definition of second normal form states that only tables with
> >> composite primary keys can be in 1NF but not in 2NF"
>
> > They have it right here. All non-key attributes must be dependent on the
> > full key. Only applies to tables with keys composed of multiple columns>
>
> No. There may be dependencies where the left side is empty.

In that case the declared candidate key is not really a candidate key. Under the assumption that the declared candidate keys are indeed candidate keys, the claim is correct.

> But it's a
> common mistake. If I remember correctly, one of my database textbooks
> "proves" that any relvar with just two attributes is automatically in BCNF.

Under the assumption that I just mentioned, that claim is actually also correct.

• Jan Hidders