presto-hive/src/main/java/io/prestosql/plugin/hive/util/Statistics.java/Statistics/mergeDecimalStatistics
class Statistics:    private static Optional<DecimalStatistics> mergeDecimalStatistics(Optional<DecimalStatistics> first, Optional<DecimalStatistics> second)
    {
        // normally, either both or none is present
        if (first.isPresent() && second.isPresent()) {
            return Optional.of(new DecimalStatistics(
                    reduce(first.get().getMin(), second.get().getMin(), MIN, true),
                    reduce(first.get().getMax(), second.get().getMax(), MAX, true)));
        }
        return Optional.empty();
    }