Re: Box query
Date: Sat, 22 Apr 2006 20:08:04 GMT
Message-ID: <E2w2g.64319$VV4.1208689_at_ursa-nb00s0.nbnet.nb.ca>
J M Davitt wrote:
> Bob Badour wrote:
>
>> J M Davitt wrote: >> >>> Bob Badour wrote: >>> >>>> Bob Badour wrote: >>>> >>>>> J M Davitt wrote: >>>>> >>>>>> Mikito Harakiri wrote: >>>>>> [snip] >>>>>>
> Regarding your "not exists (no overlap)" approach to this: I thought
> that was inspired and it got me to thinking: isn't that a universal
> quantifier? (It's been a long time since I've putzed with logic, and
> I'm feeling the urge to brush up.)
Actually, it's not so inspired as you might think. Once you get to know the sorts of problems Mikito thinks about, you will see it pops up all the time.
For instance, I believe he recently posted a puzzle regarding interval coverages where he solved the problem by finding endpoints with no overlapping intervals.
As Mikito pointed out, it features in various discussions of relational division. Humans often have difficulty with double-negatives, but computers do not.
Yes, I believe you are right about the universal quantifier thing. You could rephrase the query using "0 <= ALL select b1.high - b2.low" with the appropriate joins and restrictions (including b2.low >= b1.low). Received on Sat Apr 22 2006 - 22:08:04 CEST