presto-main/src/main/java/io/prestosql/operator/aggregation/DoubleCovarianceAggregation.java/DoubleCovarianceAggregation/covarSamp
class DoubleCovarianceAggregation:    @AggregationFunction("covar_samp")
    @OutputFunction(StandardTypes.DOUBLE)
    public static void covarSamp(@AggregationState CovarianceState state, BlockBuilder out)
    {
        if (state.getCount() <= 1) {
            out.appendNull();
        }
        else {
            double result = getCovarianceSample(state);
            DOUBLE.writeDouble(out, result);
        }
    }