wpdb num rows

1global $wpdb;
2$wpdb->get_results("
3                    SELECT * FROM " . $wpdb->prefix . "product_order 
4                        WHERE 
5                        rel = '" . $post["id"] . "' AND 
6                        `range` = '" . $range . "' AND 
7                        category = '" . $range . "'
8                "); 
9
10echo $wpdb->num_rows;
11