Re: Foreign keys
From: David Cressey <cressey73_at_verizon.net>
Date: Thu, 17 Jan 2008 21:13:18 GMT
Message-ID: <OxPjj.7796$U4.6857_at_trndny01>
Date: Thu, 17 Jan 2008 21:13:18 GMT
Message-ID: <OxPjj.7796$U4.6857_at_trndny01>
"Evan Keel" <evankeel_at_sbcglobal.net> wrote in message
news:H3Ljj.33451$4V6.12405_at_newssvr14.news.prodigy.net...
> Not reading the whole thread (big mistake on my part), but how about the
> instance where a foreign key can be null?. No functional dependecy but
> legit.
The response to this is the same as what has been given dozens of times before.
Decompose the table into two tables, one of which only contains the PK and
the FK under discussion. Now, when the FK would have received a null, omit
the entire tuple (row),
since it conveys no information.
Nulls drop out of the discussion, and it proceeds as before. Received on Thu Jan 17 2008 - 22:13:18 CET