From: | "Ivan Zolotukhin" <ivan(dot)zolotukhin(at)gmail(dot)com> |
---|---|
To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "Brendan Jurd" <direvus(at)gmail(dot)com>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: No stddev() for interval? |
Date: | 2006-05-20 16:20:17 |
Message-ID: | 751e56400605200920x712aa472g5908aae777e263b6@mail.gmail.com |
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Lists: | pgsql-general |
On 5/20/06, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Brendan Jurd" <direvus(at)gmail(dot)com> writes:
> > I noticed a peculiarity in the default postgres aggregate functions. min()=
> > ,
> > max() and avg() support interval as an input type, but stddev() and
> > variance() do not.
>
> > Is there a rationale behind this, or is it just something that was never
> > implemented?
>
> Is it sensible to calculate standard deviation on intervals? How would
> you handle the multiple components? I mean, you could certainly define
> *something*, but how sane/useful would the result be?
Strictly speaking there's nothing bad in intervals. Physically
standart deviation on interval can be very useful without any doubts.
I can make a lot of examples on this. Say you want to know stat
parameters of semi-regular periodical process (avg distance in time
between maximums of some value and stddev of this quasiperiod -- why
not?).
Regards,
Ivan Zolotukhin
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