Re: No exceptions?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 30 Jun 2006 22:16:13 GMT
Message-ID: <Nohpg.4300$pu3.101253_at_ursa-nb00s0.nbnet.nb.ca>
>
> I don't know what precisely you mean by "logical flaw", so I'll pass
> judgement. If something should be substituted for x (a "default value",
> so to speak), TABLE_DUM does seem the natural choice, though, as it
> corresponds to false/zero in some sense.
>
> "TABLE_DUM join y" evaluates to the empty relation with y's heading, not
> TABLE_DUM (unless y's header is also empty, of course).
Date: Fri, 30 Jun 2006 22:16:13 GMT
Message-ID: <Nohpg.4300$pu3.101253_at_ursa-nb00s0.nbnet.nb.ca>
[Quoted] Jon Heggland 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.
[Quoted] 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.
[Quoted] 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).
[Quoted] Surprising results with no explanation are nowhere near as useful as an informative or even instructive error message. Received on Sat Jul 01 2006 - 00:16:13 CEST