@Override
    public int getRowsRemainingAfterTerminate() throws HiveException {
      throw new UnsupportedOperationException();
    }
Retrieve the next stored intermediate result, i.e.,
Get S[x-1] in the computation of S[x..y] = S[y] - S[x-1].
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFStreamingEvaluator.java