Re: Idempotence and "Replication Insensitivity" are equivalent ?
From: <pamelafluente_at_libero.it>
Date: 19 Sep 2006 11:08:16 -0700
Message-ID: <1158689296.137909.197250_at_h48g2000cwc.googlegroups.com>
> In the case of variance and standard deviation, there's actually a
> better way than to use an accumulating aggregate function. I'd be
> willing to bet that Oracle actually does it differently; by scanning the
> data twice, once to determine the mean, and again to determine the
Date: 19 Sep 2006 11:08:16 -0700
Message-ID: <1158689296.137909.197250_at_h48g2000cwc.googlegroups.com>
Chris Smith ha scritto:
>
> In the case of variance and standard deviation, there's actually a
> better way than to use an accumulating aggregate function. I'd be
> willing to bet that Oracle actually does it differently; by scanning the
> data twice, once to determine the mean, and again to determine the
:))
this is an exaggeration. Everyone knows that the variance is simply the difference between the second moment and the square of the first moment. So you just need to accumulate values and their squares.
-P
> variance. That's *not* evaluating it as an aggregate function, whatever
> Oracle calls it.
> Chris Smith
Received on Tue Sep 19 2006 - 20:08:16 CEST