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Re: What predicates the following relation represents

From: Paul <paul_at_test.com>
Date: Sun, 04 Apr 2004 23:08:19 +0100
Message-ID: <HK%bc.30048$Y%6.3659677@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? I'm just repeating a true statement more than once, so it's not really an error.

I've just noticed an error in my previous post. I claimed the relation could be used to answer the question: "Which is the most popular batch size for purchasers of nuts?" Of course, since the relation doesn't give any information about how often batches of various sizes were sold, it can't answer this question in any meaningful way.

Paul. Received on Sun Apr 04 2004 - 17:08:19 CDT

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