@Override
    protected DateObjectInspector getValueObjectInspector(PrimitiveTypeInfo typeInfo) {
      return getValueObjectInspector();
    }
GenericUDAFDateStatsEvaluator
High/low value will be saved in stats DB as long value representing days since epoch.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFComputeStats.java