Re: Advanced SQL
Date: Fri, 7 Sep 2007 21:00:16 +0100
"Evan Keel" <evankeel_at_sbcglobal.net> wrote in message
> "David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message
>> "David Cressey" <cressey73_at_verizon.net> wrote in message
>> > There are two webistes I can recommend:
>> > For an overview to data modeling and database design.
>> > and
>> > http://www.databaseanswers.org/
>> > For about 200 free database designs, covering many common problems.
>> > will want to revise the design to suit your own requirements.
>> Call me picky but I am not entirely comfortable with that U.Texas site,
>> though it's a commendable effort overall.
>> "The relational model represents data in the form of two-dimension
>> "A relational table is a flat file ..."
>> "Primary and foreign keys are the most basic components on which
>> theory is based."
>> "The definition of second normal form states that only tables with
>> 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>
>> "The third normal form requires that all columns in a relational table
>> dependent only upon the primary key"
> They have it right again. No transitive dependecies. So the problem? Oh
> remove the candidate key in this test.
>> David Portas
Normalization is concerned with candidate keys not just primary keys, so the definitions are necessary conditions but not sufficient ones.
-- David PortasReceived on Fri Sep 07 2007 - 22:00:16 CEST