static boolean satisfyPrecondition(Statistics stats) {
    return stats != null && stats.getBasicStatsState().equals(Statistics.State.COMPLETE)
        && !stats.getColumnStatsState().equals(Statistics.State.NONE);
  }
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