@Override
  public String getDisplayString(String[] children) {
    return "SURROGATE_KEY()";
  }
This function is not a deterministic function, and not a runtime constant.
The return value is sequence within a query with a unique staring point based on write_id and task_id
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFSurrogateKey.java