Standard Deviation for SQLite

Question

I\'ve searched the SQLite docs and couldn\'t find anything, but I\'ve also searched on Google and a few results appeared.

Does SQLite have any built-in Standard Devi

Answer 1

added some error detection in the python functions

class StdevFunc:
    """
    For use as an aggregate function in SQLite
    """
    def __init__(self):
        self.M = 0.0
        self.S = 0.0
        self.k = 0

    def step(self, value):
        try:
            # automatically convert text to float, like the rest of SQLite
            val = float(value) # if fails, skips this iteration, which also ignores nulls
            tM = self.M
            self.k += 1
            self.M += ((val - tM) / self.k)
            self.S += ((val - tM) * (val - self.M))
        except:
            pass

    def finalize(self):
        if self.k <= 1: # avoid division by zero
            return none
        else:
            return math.sqrt(self.S / (self.k-1))