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## Re: variance aggregates per SQL:2003

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On Tue, Mar 07, 2006 at 07:56:06PM -0500, Neil Conway wrote: > On Tue, 2006-03-07 at 16:36 -0800, David Fetter wrote: > > The rationale is kinda mathematical. A measure of deviation from > > central tendency (i.e. variance or stddev) is something where you > > probably don't want to normalize the weights. > > > > For example, the standard deviation of {0,1,1,1,2} is about 0.707, > > but the standard deviation of {0,1,2} is 1. > > Well, I realize that stddev(DISTINCT x) != stddev(x) and that most > people are going to be interested in stddev(x), but I don't think > it's inconceivable for someone to be interested in stddev(DISTINCT > x). Not inconceivable. Just really hard to justify unless you're trying to fudge a number ;) > Explicitly checking for and rejecting it doesn't serve any useful > purpose that I can see, beyond compliance with the letter of the > standard -- if the user asks for stddev(DISTINCT x), are we really > providing useful behavior if we refuse to calculate it? Nope. I was just coming up for a rationale for why the standard disallows it :) Cheers, D -- David Fetter david(at)fetter(dot)org http://fetter.org/ phone: +1 415 235 3778 Remember to vote!

- Re: variance aggregates per SQL:2003 at 2006-03-08 00:56:06 from Neil Conway

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