Re: BCNF: superkey or candidate key ?

"Jan Hidders" <hidders_at_gmail.com> wrote in message news:1159257366.662041.197990_at_h48g2000cwc.googlegroups.com...

> I assume you are talking about the case where R has only two columns.
> Indeed, then it has only trivial FDs and is in BCNF. All the
> definitions agree on that, of course, because they are equivalent.

I'm interested in the case where R has n columns, and the primary key has n-1 columns.
Is there anything in particular that applies to that case, and not to cases with more than one non-key
column?

Here's what's behind my question. relational tables with at most 1 non-key column is where the great debate about NULLs becomes moot. If you want to leave the non-key column NULL, then just omit the row. Of course, you need another table with just the primary key to keep track of which of the possible primary keys are in existence. Received on Tue Sep 26 2006 - 14:31:22 CEST