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"x" <x-false_at_yahoo.com> wrote in message news:40d8642c_at_post.usenet.com...
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> > > > 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
> at
> > > > least less fundamental) operators.
> But not all bag operators can be decomposed in this way.
Let's go through the list:
AVG - nonfundamental, can be expressed in terms of SUM
STDDEV = SQRT(VARIANCE)
VARIANCE = (SUM(x*x)-(SUM(x)*SUM(x))/SUM(1))/(SUM(1)-1)
Do you need mere examples to be convinced that there are only 4 fundamental aggregate operators?
1. SUM = "+"* 2. MIN = "/\"* 3. MAX = "\/"* 4. LIST = "||"*
> > >
> > > > How does COUNT(distinct x) fits in? It's just abuse of syntax by
those who
are reluctant to write a slightly lengthier expression with inline view.
Slight correction: It's just abuse of syntax by those who are reluctant to write a slightly lengthier [but more presize] expression with inline view. Received on Tue Jun 22 2004 - 12:14:47 CDT