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Re: No exceptions?

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 30 Jun 2006 22:16:13 GMT
Message-ID: <Nohpg.4300$pu3.101253@ursa-nb00s0.nbnet.nb.ca>


Jon Heggland wrote:

> paul c wrote:
>

>>Let me re-phrase my original question:  Is there a logical flaw in
>>substituting TABLE_DUM for x in the expression "x join y" when x is not
>>in the catalogue?

>
> I don't know what precisely you mean by "logical flaw", so I'll pass
> judgement. If something should be substituted for x (a "default value",
> so to speak), TABLE_DUM does seem the natural choice, though, as it
> corresponds to false/zero in some sense.

But then, what about expressions like "y minus x" where x is unknown? What if y and x were intended to both be very large relations with a small difference? The result would go from small to very large.

Similarly for "not exists" expressions.

>>(Assuming that the syntax requires x to be a relation and with the whole
>>expression's value being TABLE_DUM as well and granting that such a
>>result might seem surprising to most people.)

>
> "TABLE_DUM join y" evaluates to the empty relation with y's heading, not
> TABLE_DUM (unless y's header is also empty, of course).

Surprising results with no explanation are nowhere near as useful as an informative or even instructive error message. Received on Fri Jun 30 2006 - 17:16:13 CDT

Original text of this message

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