Best practice for returning "error" from a function
===

I have a function:

    public function CustomerRating() {
         $result = $db->query("...");
         $row = $result->fetch_assoc();
         
         if($row)
              $output = $row['somefield'];
         } else {
              $output = "error";
         }
         
         return $output;
    }

    //somewhere on another page...
    if(is_numeric($class->CustomerRating()) {
         echo $class->CustomerRating;
    } else {
          echo "There is an error with this rating.";
    }

Is there a better way to find errors? In this function, if no rows are returned, it doesn't mean an "error" per se, it simply means the value can't be calculated. When I check for the result of a function, I feel like there is a better way to check the data being returned before I display it in the if function. What's the best way to do this? I'd like to return a "false", but how would I check for that when calling the function? Thanks!