presto-main/src/main/java/io/prestosql/operator/aggregation/CentralMomentsAggregation.java/CentralMomentsAggregation/skewness
class CentralMomentsAggregation:    @AggregationFunction("skewness")
    @Description("Returns the skewness of the argument")
    @OutputFunction(StandardTypes.DOUBLE)
    public static void skewness(@AggregationState CentralMomentsState state, BlockBuilder out)
    {
        long n = state.getCount();

        if (n < 3) {
            out.appendNull();
        }
        else {
            double result = Math.sqrt(n) * state.getM3() / Math.pow(state.getM2(), 1.5);
            DOUBLE.writeDouble(out, result);
        }
    }