CODE EXAMPLE FOR PHP

wpdb num_rows

global $wpdb;
$wpdb->get_results("
                    SELECT * FROM " . $wpdb->prefix . "product_order 
                        WHERE 
                        rel = '" . $post["id"] . "' AND 
                        `range` = '" . $range . "' AND 
                        category = '" . $range . "'
                "); 

echo $wpdb->num_rows;