public String addAllColStats(ColumnStatisticsData columnStatisticsData) {
    List<String> temp = new ArrayList<>();
    addBinaryStats(columnStatisticsData, temp);
    addLongStats(columnStatisticsData, temp);
    addBooleanStats(columnStatisticsData, temp);
    addStringStats(columnStatisticsData, temp);
    addDateStats(columnStatisticsData, temp);
    addDoubleStats(columnStatisticsData, temp);
    addDecimalStats(columnStatisticsData, temp);
    return Joiner.on(",").join(temp);
  }
Checks whether the column statistics data stores histogram statistics, and returns its base64 encoding if so.
@param cd the column statistics data
@return the base64 encoding of the histogram statistics if existing, null otherwise.
ql/src/java/org/apache/hadoop/hive/ql/exec/DDLPlanUtils.java