Much Ado about Nothing
From: David Cressey <david_at_dcressey.com>
Date: Sat, 24 Feb 2001 12:45:18 GMT
Message-ID: <y1Ol6.35885$2X4.120721_at_petpeeve.ziplink.net>
Date: Sat, 24 Feb 2001 12:45:18 GMT
Message-ID: <y1Ol6.35885$2X4.120721_at_petpeeve.ziplink.net>
Onward.
NULLS don't belong in relations.
By definition, every attribute of every tuple of every relation is a value drawn from the corresponding domain. By definition, a NULL is not a value, but a marker indicating the absence of a value. So you can't put a NULL in a relation.
This illustrates the difference between what I'll call "the SQL model of data" and the relational model of data. A lot of practical types like myself walk around with the SQL model of data in our heads, imagining it to be the same thing as the relational model of data.
They aren't the same.
--
Regards,
David Cressey
www.dcressey.com
Received on Sat Feb 24 2001 - 13:45:18 CET