@Override
  public <R, C> R accept(PlanVisitor<R, C> visitor, C context) {
    return visitor.visitGroup(this, context);
  }
orderingScheme may include two parts: PartitionKey and OrderKey. It marks the number of
PartitionKey.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/node/GroupNode.java