Re: Examples of SQL anomalies?
Date: Wed, 02 Jul 2008 10:26:56 -0300
Ed Prochak wrote:
> On Jun 30, 5:54 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
>>On Jun 30, 10:31 am, "Brian Selzer" <br..._at_selzer-software.com> wrote: >> >> >> >> >>>Well, the OP wanted examples of SQL anomalies, and you've just confirmed a >>>big one. >> >>>If you have a bag that can contain peaches, but doesn't, then the answer to >>>the question "How many peaches are in the bag?" is clearly zero. If you are >>>asked by the accountant, "How much were we billed by AT&T this month?" but >>>AT&T didn't send a bill, then the answer is clearly zero. That SQL's COUNT >>>and SUM are something other than these common sense usages exemplifies their >>>anomalous nature. >> >>[I meant to say this in my other post, but] >> >>Brian gets it exactly right here. >> >>Marshall
> I'm not so sure about the AT&T bill. Consider the question may be
> badly phrased:
> "How much were we billed by AT&T this month?"
> Is the amount being sought the amount on the bill received this month?
> or the amount for this month's services?
> If the question is asked July 1 and we haven't got the bill in the
> mail yet, the answer must be "I don't know."
> And who is the "we"? Are there multiple entities involved? (multiple
> businesses owned by one parent company with separate phone accounts/
> bills? or maybe a home business and personal home phone account both
> shown on one bill?)
> So even in real life NULL (aka "I don't know") happens to be the
> correct answer to some questions. It is not as clean cut as you and
> Brian would like.
You are suggesting the computer should have some way to evaluate external predicates. The computer cannot. Your argument is a red herring.
If one expects a bill and the total is 0, that's just as useful to alert one that the bill has not yet arrived as a NULL would be. Received on Wed Jul 02 2008 - 08:26:56 CDT