php中面向对象删除数据

<?php
header("Content-Type: text/html;charset=utf-8");
include_once("comm.php");

$id = isset($_POST["m_id"]) ? intval($_POST["m_id"]) : intval("0");
/*echo gettype($id);*/
$sql = "DELETE FROM `message` WHERE `message`.`m_id` =".$id;
		$result = $conn ->query($sql);
		$mark = $conn -> affected_rows;
		/*echo $mark;*/
	if (!$result || $mark == 0) {
			echo "删除失败!";
			exit ;
		}
		echo "删除成功!";
		$conn -> close();
?>