presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitSetOperation
class DefaultTraversalVisitor:    @Override
    protected R visitSetOperation(SetOperation node, C context)
    {
        for (Relation relation : node.getRelations()) {
            process(relation, context);
        }
        return null;
    }