Intervals, stddev() and alerting

I want to create alerts based on the standard deviation (stddev) of a query. The query uses default GROUP BY function, time($__inteval), and the alert is condition is avg() of query(A, 1m, now).

Through trial-and-error I’ve learned the query fails because the default GROUP BY function time($__interval) chooses intervals shorter than my acquisition rate. That means the alert evaluation always fails because the standard deviation of a single point (or no points) is null.

My solution is to specify Min time interval = 2*(acquisition rate) to ensure the returned queries always contain at least two points… but that seems hacky.

Is there a better way to ensure stddev() evaluates on a two or more points, so it does not produce false null data alerts?