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RE: [HACKERS] Standard Deviation function.

From: "Stupor Genius" <stuporg(at)erols(dot)com>
To: "Hackers" <pgsql-hackers(at)postgresql(dot)org>
Cc: "Bruce Momjian" <maillist(at)candle(dot)pha(dot)pa(dot)us>
Subject: RE: [HACKERS] Standard Deviation function.
Date: 1998-06-05 03:22:09
Message-ID: 000001bd9031$1fe5e800$d39daccf@darren (view raw or flat)
Thread:
Lists: pgsql-hackers
> > > I really need a Standard Deviation aggregate function...
> > 
> > I thought about this a long time ago and had an idea but never
> > got around to trying to implement it.  I was going to have some
> > functions that worked on a structure of two doubles to track
> > the sum and square instead of using only one simple type.
> 
> I remember talking about this to someone, and the problem is that you
> needed the average WHILE scanning through the table, which required two
> passes, which the aggregate system is not designed to do.  I may be
> wrong on this, though.

I had asked you how to calculate this and the variance early last
year.  One (I think the variance) was two-pass because of the need
for the average, but I thought the StdDev would work with the struct.

Been a while and I still haven't configured #(*&^ FreeBSD ppp yet.

darrenk

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