public static double calculateStdSampleResult(double variance, long count) {
      return Math.sqrt(variance / (count - 1));
    }
Compute the sample standard deviation by extending
GenericUDAFVarianceEvaluator and overriding the terminate() method of the
evaluator.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFStdSample.java