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## Re: variance aggregates per SQL:2003

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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). 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? -Neil

- Re: variance aggregates per SQL:2003 at 2006-03-08 00:36:04 from David Fetter

- Re: variance aggregates per SQL:2003 at 2006-03-08 00:58:47 from David Fetter
- Re: variance aggregates per SQL:2003 at 2006-03-08 03:25:33 from Tom Lane

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