private boolean isFlatten(RexNode rexNode) {
    return rexNode instanceof RexCall && ((RexCall) rexNode).op instanceof SqlUserDefinedFunction
        && ((RexCall) rexNode).op.getName().equalsIgnoreCase("flatten");
  }
Updates the Diagnostics Metrics (processing time and number of events)
@param arrivalTime input message arrival time (= beging of processing in this operator)
@param outputTime output message output time (=end of processing in this operator)
@param isNewInputMessage whether the input Message is from new input message or not
samza-sql/src/main/java/org/apache/samza/sql/translator/ProjectTranslator.java