Re: No stddev() for interval?

> If the intervals are all expressed in seconds then sure, the calculation
> is straightforward and useful. I'm wondering what happens when nonzero
> values of days and months get in there.
>
> regards, tom lane
>

The existing logic used in avg(interval) can be seen in
backend/utils/adt/timestamp.c, refer to functions interval_accum,
interval_avg and interval_div.

interval_div(interval, double) is the most interesting for this discussion.
There is a helpful comment that reads /* evaluate fractional months as 30
days */.

So for example, interval_div('4 mons'::interval, 3) gives you '1 mon 10
days'.

It's not perfect, but doing arithmetic that involves converting between
months and days never is. All in favour of deleting the month as unit of
measurement of time say "aye".

Well that's not going to happen in my lifetime. How about we just extend
this same logic over to stddev and variance? It's strange having avg but
not the other two.

Regards,
BJ