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Re: What predicates the following relation represents

From: Paul Vernon <paul.vernon_at_ukk.ibmm.comm>
Date: Tue, 6 Apr 2004 13:40:46 +0100
Message-ID: <c4u8li$106q$1@gazette.almaden.ibm.com>


"Paul" <paul_at_test.com> wrote in message
news:HK%bc.30048$Y%6.3659677_at_wards.force9.net...
> --CELKO-- wrote:
> > If what we are calling "sales" in this example ought to be
> > "batch_size", then I have it. And my key would be both columns, as
> > you said.
>
> yep that was what I was meaning.
>
> Also the predicate could have been: "packets of PART are available for
> sale in batches of size SOLD". It's kind of pointless discussing whether
> relations are "legal" without knowing the real-world interpretation of
> the underlying predicate.
>
> Here's another question:
> Suppose I have a relation containing the tuple ('nuts', 25).
> If I then do an INSERT of the tuple ('nuts', 25) in SQL I get an key
> violation error (assuming the primary key is defined). In a truly
> relational DBMS, should it silently accept this, but just do nothing?

In a truly relational database, INSERT is a derived concept. Specifically it is a shorthand for an assignment. Whether or not you include a check for 'key violation' in that shorthand is of little import IMO.

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Tue Apr 06 2004 - 07:40:46 CDT

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