private boolean validRexCall(RexCall call) {
      if (call instanceof RexOver) {
        LOG.debug("RexOver operator push down is not supported for now with the following operator:" + call);
        return false;
      }
      final SqlOperator operator = call.getOperator();
      if (HiveIn.INSTANCE.equals(operator)) {
        return true;
      }
      List <RexNode> operands = call.getOperands();
      RelDataType resType = call.getType();
      ArrayList<RelDataType> paramsListType = new ArrayList<RelDataType>();
      for (RexNode currNode : operands) {
        paramsListType.add(currNode.getType());
      }
      return dialect.supportsFunction(operator, resType, paramsListType);
    }
A utility class that helps identify Hive-Jdbc functions gaps.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/jdbc/JDBCRexCallValidator.java