Re: does a table always need a PK?

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.

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