presto-main/src/main/java/io/prestosql/cost/ExchangeStatsRule.java/ExchangeStatsRule/mapToOutputSymbols
class ExchangeStatsRule:    private PlanNodeStatsEstimate mapToOutputSymbols(PlanNodeStatsEstimate estimate, List<Symbol> inputs, List<Symbol> outputs)
    {
        checkArgument(inputs.size() == outputs.size(), "Input symbols count does not match output symbols count");
        PlanNodeStatsEstimate.Builder mapped = PlanNodeStatsEstimate.builder()
                .setOutputRowCount(estimate.getOutputRowCount());

        for (int i = 0; i < inputs.size(); i++) {
            mapped.addSymbolStatistics(outputs.get(i), estimate.getSymbolStatistics(inputs.get(i)));
        }

        return mapped.build();
    }