presto-main/src/main/java/io/prestosql/sql/planner/plan/DistinctLimitNode.java/DistinctLimitNode/getOutputSymbols
class DistinctLimitNode:    @Override
    public List<Symbol> getOutputSymbols()
    {
        ImmutableList.Builder<Symbol> outputSymbols = ImmutableList.builder();
        outputSymbols.addAll(distinctSymbols);
        hashSymbol.ifPresent(outputSymbols::add);
        return outputSymbols.build();
    }