Re: NULLs: theoretical problems?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 24 Aug 2007 20:53:31 -0300
Message-ID: <46cf6f34$0$4021$9a566e8b_at_news.aliant.net>
>
>
> Because it does not satisify all the logical laws of an AND, so to
> avoid confusion another notation is used. Since it's related to an
> existential quantifier a similar notation was chosen (think of EXISTS
> x : f).
>
> And, yes, as Jon correctly remarked it is in fact equivalent with
> something you can already write in SQL so you could achieve the same
> with some self-discipline.
Date: Fri, 24 Aug 2007 20:53:31 -0300
Message-ID: <46cf6f34$0$4021$9a566e8b_at_news.aliant.net>
Jan Hidders wrote:
> On 24 aug, 16:35, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
>
>>Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote innews:famjo6$i68$1_at_orkan.itea.ntnu.no: >> >> >>>In other words, the DEF query is equivalent to >> >>>SELECT * FROM t WHERE t.a IS NOT NULL AND (t.a = 5 OR TRUE) >> >>My understanding was that the DEF as written was a shorthand: >> >>e.g. >>'def(x):((x or y) and x)' -> '((def(x) or y) and def(x))' >> >>You may be right, but then why the formula was not written with an >>explicit 'and' ?
>
>
> Because it does not satisify all the logical laws of an AND, so to
> avoid confusion another notation is used. Since it's related to an
> existential quantifier a similar notation was chosen (think of EXISTS
> x : f).
>
> And, yes, as Jon correctly remarked it is in fact equivalent with
> something you can already write in SQL so you could achieve the same
> with some self-discipline.
Let me suggest the use of 6th normal form and then EXISTS is all one would need. Received on Sat Aug 25 2007 - 01:53:31 CEST