public void add(ColStatistics stat) {
    if (!inited) {
      inited = true;
      result = stat.clone();
      result.setRange(null);
      result.setIsEstimated(true);
      return;
    } else {
      if (stat.getAvgColLen() > result.getAvgColLen()) {
        result.setAvgColLen(stat.getAvgColLen());
      }
      if (stat.getCountDistint() > result.getCountDistint()) {
        result.setCountDistint(stat.getCountDistint());
      }
      if (stat.getNumNulls() > result.getNumNulls()) {
        result.setNumNulls(stat.getNumNulls());
      }
      if (stat.getNumTrues() > result.getNumTrues()) {
        result.setNumTrues(stat.getNumTrues());
      }
      if (stat.getNumFalses() > result.getNumFalses()) {
        result.setNumFalses(stat.getNumFalses());
      }
      if (stat.isFilteredColumn()) {
        result.setFilterColumn();
      }

    }

  }
Combines {@link ColStatistics} objects to provide the most pessimistic estimate.
ql/src/java/org/apache/hadoop/hive/ql/stats/estimator/PessimisticStatCombiner.java