presto-main/src/main/java/io/prestosql/cost/PlanNodeStatsEstimateMath.java/PlanNodeStatsEstimateMath/addStats
class PlanNodeStatsEstimateMath:    private static PlanNodeStatsEstimate addStats(PlanNodeStatsEstimate left, PlanNodeStatsEstimate right, RangeAdditionStrategy strategy)
    {
        if (left.isOutputRowCountUnknown() || right.isOutputRowCountUnknown()) {
            return PlanNodeStatsEstimate.unknown();
        }

        PlanNodeStatsEstimate.Builder statsBuilder = PlanNodeStatsEstimate.builder();
        double newRowCount = left.getOutputRowCount() + right.getOutputRowCount();

        concat(left.getSymbolsWithKnownStatistics().stream(), right.getSymbolsWithKnownStatistics().stream())
                .distinct()
                .forEach(symbol -> {
                    SymbolStatsEstimate symbolStats = SymbolStatsEstimate.zero();
                    if (newRowCount > 0) {
                        symbolStats = addColumnStats(
                                left.getSymbolStatistics(symbol),
                                left.getOutputRowCount(),
                                right.getSymbolStatistics(symbol),
                                right.getOutputRowCount(),
                                newRowCount,
                                strategy);
                    }
                    statsBuilder.addSymbolStatistics(symbol, symbolStats);
                });

        return statsBuilder.setOutputRowCount(newRowCount).build();
    }