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