@Override
  public Operator visitCountMerge(CountSchemaMergeNode node, LocalExecutionPlanContext context) {
    List<Operator> children = dealWithConsumeChildrenOneByOneNode(node, context);
    OperatorContext operatorContext =
        context
            .getDriverContext()
            .addOperatorContext(
                context.getNextOperatorId(),
                node.getPlanNodeId(),
                CountMergeOperator.class.getSimpleName());
    if (node.getChildren().get(0) instanceof LevelTimeSeriesCountNode) {
      return new CountGroupByLevelMergeOperator(operatorContext, children);
    } else {
      return new CountMergeOperator(operatorContext, children);
    }
  }
This Visitor is responsible for transferring PlanNode Tree to Operator Tree.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/OperatorTreeGenerator.java