presto-main/src/main/java/io/prestosql/sql/planner/planprinter/PlanPrinter.java/PlanPrinter/visitOutput
class PlanPrinter:        @Override
        public Void visitOutput(OutputNode node, Void context)
        {
            NodeRepresentation nodeOutput = addNode(node, "Output", format("[%s]", Joiner.on(", ").join(node.getColumnNames())));
            for (int i = 0; i < node.getColumnNames().size(); i++) {
                String name = node.getColumnNames().get(i);
                Symbol symbol = node.getOutputSymbols().get(i);
                if (!name.equals(symbol.toString())) {
                    nodeOutput.appendDetailsLine("%s := %s", name, symbol);
                }
            }
            return processChildren(node, context);
        }