Re: Counting propositions
Date: Tue, 22 Jun 2004 19:57:42 +0300
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"Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message
> "x" <x-false_at_yahoo.com> wrote in message
> > **** Post for FREE via your newsreader at post.usenet.com ****
> > "Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message
> > news:DPYBc.18$da4.141_at_news.oracle.com...
> > >
> > > "Paul" <paul_at_test.com> wrote in message
> > > news:CFWBc.19053$NK4.3265189_at_stones.force9.net...
> > > > Isn't "select count(*)" a similar thing? You should explicitly name
> > > > data columns you want. If you change the candidate keys it may
> > > > the whole interpretation of the propositions. In which case it may
> > > > longer be true that you want to count propositions.
> > >
> > > Count is unusual aggregate operator. Every other aggregate operator is
> > > associated with a binary operation. Indeed, the SUM is iterative
> > application
> > > of "+", the MAX is iterative application of "max(x,y)" (or CASE ...).
> > There
> > > are few exceptions like AVG, but they can be viewed as redundant (or
> > > least less fundamental) operators.
> > SUM(),MAX(),AVG() apply to a bag of values.
> > > What operation COUNT is application of? The increment, of course.
> > the
> > > examples above, the increment is unary operation, so the COUNT
> > > really have an argument!
> > COUNT() apply to a bag of values.
> SUM(a,b,c,d) = ((a + b) + c) + d
> where brackets are inessential, as "+" is associative operators.
> I'm talking about expressing an operation with variable number of
> in terms of binary operation.
I understood this.
But not all bag operators can be decomposed in this way.
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