presto-main/src/main/java/io/prestosql/operator/aggregation/MergeQuantileDigestFunction.java/MergeQuantileDigestFunction/combine
class MergeQuantileDigestFunction:    @CombineFunction
    public static void combine(QuantileDigestState state, QuantileDigestState otherState)
    {
        merge(state, otherState.getQuantileDigest());
    }