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## Re: variance aggregates per SQL:2003

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On Tue, Mar 07, 2006 at 05:54:00PM -0500, Neil Conway wrote: > This patch implements some new aggregate functions defined by SQL2003: > stddev_pop(), stddev_samp(), var_pop(), and var_samp(). stddev_samp() > and var_samp() are identical to the existing stddev() and variance() > aggregates, so I've made the latter aliases for the former. > > I noticed that SQL2003 does not allow DISTINCT to be specified for these > aggregate functions. I can't really see the rationale for this > restriction, and it would be fairly ugly to implement as far as I can > tell. Thoughts? > 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. Cheers, D (still hoping for some way to extend stddev, etc. to intervals) -- David Fetter david(at)fetter(dot)org http://fetter.org/ phone: +1 415 235 3778 Remember to vote!

- variance aggregates per SQL:2003 at 2006-03-07 22:54:00 from Neil Conway

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

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