Re: does a table always need a PK?

"Heikki Tuuri" <Heikki.Tuuri_at_innodb.com> wrote in message news:GEg2b.11$G37.0_at_read3.inet.fi...
> Hi!
>
> "Christopher Browne" <cbbrowne_at_acm.org> kirjoitti viestissä
> news:bibhbj$7hssg$1_at_ID-125932.news.uni-berlin.de...
> > After a long battle with technology,"Heikki Tuuri"
> <Heikki.Tuuri_at_innodb.com>, an earthling, wrote:
> > > I would like to bring up to the discussion what I remarked in the
other
> > > discussion thread on MySQL RDBMSness.
> > >
> > > If we have a quantum mechanical system where electrons are
> > > indistinguishable, would it not be natural to create a table of
> electrons
> > > without a primary key?
> >
> > In a non-relational system, sure.
> >
> > In a relational database, as per Codd's definition,
> >
> > "Each and every datum (atomic value) in a relational database is
> > guaranteed to be logically accessible by resorting to a table name,
> > primary key value, and column name."
> >
> > Thus, for a system to be considered relational, there must be, by
> > definition, a primary key.
> >
> > Of course, MySQL AB doesn't claim to sell a relational database (the
> > word "relational" is not used anywhere on the main web page), so
> > perhaps MySQL might be the preferable database system for managing
> > those sorts of things.
>
> In the manual they claim to sell one:
>
> http://www.mysql.com/doc/en/What-is.html
> "
> MySQL is a relational database management system.
> "
>
> I think in all SQL databases you can create a table without a primary key.
>
> 2 years ago we discussed the 'correct' definition of 'relational' in
> comp.databases.theory with several people. I think the concept is vague.
For
> example, Codd's 12 principles are not formulated as mathematical axioms.

Read the 1970 ACM paper instead of 12 rules of thumb. Received on Mon Aug 25 2003 - 16:19:43 CEST