@Override
  public PlanNode clone() {
    return new AggregationNode(
        id, null, aggregations, groupingSets, preGroupedSymbols, step, hashSymbol, groupIdSymbol);
  }
@return whether this node should produce default output in case of no input pages. For example
    for query:
    <p>SELECT count(*) FROM nation WHERE nationkey < 0
    <p>A default output of "0" is expected to be produced by FINAL aggregation operator.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/node/AggregationNode.java