Re: Aggregate Function corr does not always return the correct value

Maxim Orlov <orlovmg(at)gmail(dot)com> writes:
> One of the clients complained as to why the query for calculating the
> correlation coefficient with the CORR function yielded such weird
> results. After a little analysis, it was discovered that they were
> calculating the correlation coefficient for two sets, one of which is
> more or less random and the other of which is simply a set of constant
> values (0.09 if that matters). As a result, they were attaining
> unexpected results. However, as far as I am aware, they should have
> received NULL because it is impossible to calculate the standard
> deviation for such a set.

[ shrug... ] Calculations with float8 are inherently inexact, so
it's unsurprising that we sometimes fail to detect that the input
is exactly a horizontal or vertical line. I don't think there is
anything to be done here that wouldn't end in making things worse.

regards, tom lane