@Override
  public Operator visitPlan(PlanNode node, LocalExecutionPlanContext context) {
    throw new UnsupportedOperationException("should call the concrete visitXX() method");
  }
This Visitor is responsible for transferring Table PlanNode Tree to Table Operator Tree.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/TableOperatorGenerator.java