@Override
  public Operator visitEnforceSingleRow(
      EnforceSingleRowNode node, LocalExecutionPlanContext context) {
    Operator child = node.getChild().accept(this, context);
    OperatorContext operatorContext =
        context
            .getDriverContext()
            .addOperatorContext(
                context.getNextOperatorId(),
                node.getPlanNodeId(),
                EnforceSingleRowOperator.class.getSimpleName());

    return new EnforceSingleRowOperator(operatorContext, child);
  }
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