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Re: [Gnumed-devel] NULLS was: Consolidation Proposal: ClearHealth, FreeM

From: Karsten Hilbert
Subject: Re: [Gnumed-devel] NULLS was: Consolidation Proposal: ClearHealth, FreeMED and OpenEMR
Date: Sun, 10 Jul 2005 18:50:06 +0200
User-agent: Mutt/1.5.9i

On Wed, Jul 06, 2005 at 04:25:05PM -0700, Tim Cook wrote:

> On Wed, 2005-06-15 at 17:41 +0200, Karsten Hilbert wrote:
> > > > > 3) do you allow any nulls in your database?
> > > > Yes, hopefully only where appropriate. Please do point out any
> > > > flaws you find.
> > > There are no appropriate places for NULLS in a "relational" data
> > model.
> > Not in a "pure" relational model, true. I do think great care
> > needs to be taken when using NULLs. All in all it's a
> > religious issue.
> No. It is not a religious issue at all.  It is a logical issue that
> relates to the SQL deficiency.  For quick insight; review the fact that
> the WHERE clause, by definition returns a True or a False.  What happens
> when a NULL is an attribute value as the subject of the WHERE?

I do not understand the issue all too well, apparently. Can you give
a simple hands-on example in terms of real tables and real data
that clearly shows were using NULLs falls down *logically* ?

> Otherwise your relations aren't atomic and your application code must be
> created to handle these exceptions.
Why of course. No doubt about that.

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