Re: Normalization and Derived Information

From: Tony <andrewst_at_onetel.com>
Date: 13 Oct 2004 02:01:44 -0700
Message-ID: <ed8a00fa.0410130101.2be5ee16_at_posting.google.com>


Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net> wrote in message news:<b6ogkc.34m.ln_at_mercury.downsfam.net>...
> Tony Andrews wrote:
> > Now in case (1) the total is sure to be right, whereas in (2) it could
> > be wrong because our stored total has somehow got out of sync with the
> > detail data. Yet this is somehow seen as a "good thing", because if we
> > add up all the details and find that that DO agree with the stored
> > total (as they should), we somehow have more confidence in the total.
> > Why? I am sure I must be missing something.
>
> The total in case 1 is sure to be wrong, which I state from the experience
> of watching it happen. This is because it is very easy to consider the
> case of extended price = price * qty, and from there to imagine that Order
> Total = SUM(extended price). What could go wrong, right? Who could mess
> that up?

Well, that wasn't quite what I meant. The case (1) total should be provided by a mechanism such as a view - as if it were a stored total, but not actually stored. I'm not suggesting it is better if users work the total out for themselves!

I agree with a lot of what you say though. Received on Wed Oct 13 2004 - 11:01:44 CEST

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