VAR_POP returns the population variance of a set of numbers after discarding the nulls in this set. The expr is a number expression, and the function returns a value of type NUMERIC. If the function is applied to an empty set, then it returns null. The function makes the following calculation:
(SUM(expr2) - SUM(expr)2 / COUNT(expr)) / COUNT(expr)
The function returns a value of type NUMERIC. If the function is applied to an empty set, then it returns null.