presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/visitJoin
class GraphvizPrinter:        @Override
        public Void visitJoin(JoinNode node, Void context)
        {
            List<Expression> joinExpressions = new ArrayList<>();
            for (JoinNode.EquiJoinClause clause : node.getCriteria()) {
                joinExpressions.add(clause.toExpression());
            }

            String criteria = Joiner.on(" AND ").join(joinExpressions);
            printNode(node, node.getType().getJoinLabel(), criteria, NODE_COLORS.get(NodeType.JOIN));

            node.getLeft().accept(this, context);
            node.getRight().accept(this, context);

            return null;
        }