presto-tpch/src/main/java/io/prestosql/plugin/tpch/statistics/StatisticsEstimator.java/StatisticsEstimator/addPartitionStats
class StatisticsEstimator:    private TableStatisticsData addPartitionStats(TableStatisticsData left, TableStatisticsData right, TpchColumn<?> partitionColumn)
    {
        Map<String, ColumnStatisticsData> combinedColumnStats = left.getColumns().entrySet().stream().collect(toImmutableMap(
                Map.Entry::getKey,
                entry -> {
                    String columnName = entry.getKey();
                    ColumnStatisticsData leftStats = entry.getValue();
                    ColumnStatisticsData rightStats = right.getColumns().get(columnName);
                    Optional<Long> ndv = addDistinctValuesCount(partitionColumn, columnName, leftStats, rightStats);
                    Optional<Object> min = combine(leftStats.getMin(), rightStats.getMin(), this::min);
                    Optional<Object> max = combine(leftStats.getMax(), rightStats.getMax(), this::max);
                    // Sum data sizes only if both known
                    Optional<Long> dataSize = leftStats.getDataSize()
                            .flatMap(leftDataSize -> rightStats.getDataSize().map(rightDataSize -> leftDataSize + rightDataSize));
                    return new ColumnStatisticsData(ndv, min, max, dataSize);
                }));

        return new TableStatisticsData(
                left.getRowCount() + right.getRowCount(),
                combinedColumnStats);
    }