private static boolean isAllParentsContainStatistics(Operator<? extends OperatorDesc> op) {
    for (Operator<? extends OperatorDesc> parent : op.getParentOperators()) {
      if (parent.getStatistics() == null) {
        return false;
      }
    }
    return true;
  }
Default rule is to aggregate the statistics from all its parent operators.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java