Tom Lane wrote:
> AFAICS, stddev/variance require the concept of multiplying two input
> values together (square, and also square root, are in the formulas).
> I don't know what it means to multiply two intervals --- there's no
> such operator in Postgres, anyway.
The problem is not much different than recording temperature
measurements in a numeric column and then taking the standard
deviation. Kelvin squared does not make much sense, but it's only an
intermediate quantity.
The problem is that an interval datum already implies the units, so in
order to allow interval * interval we would have to add a new type
"interval squared", which would probably be considered to be a bit
foolish.