private static void mergeColumnStats(Map<String, ColumnStatisticsObj> oldStats,
      ColumnStatistics newStats) {
    List<ColumnStatisticsObj> newColList = newStats.getStatsObj();
    if (newColList != null) {
      for (ColumnStatisticsObj colStat : newColList) {
        // This is admittedly a bit simple, StatsObjectConverter seems to allow
        // old stats attributes to be kept if the new values do not overwrite them.
        oldStats.put(colStat.getColName().toLowerCase(), colStat);
      }
    }
  }
@param dbName actual database name
@param tblName actual table name or search pattern (for error message)
ql/src/java/org/apache/hadoop/hive/ql/metadata/SessionHiveMetaStoreClient.java