php实现留言板功能（会话控制）

<?php
session_start();
$UserName = $_SESSION["UserName"];
$jsr = $_POST["jsr"];
$nr = $_POST["neirong"];
$Times = date("Y-m-d H:i:s");


require"DBDA.class.php";
$db = new DBDA();
$sql = "insert into liuyan values('','{$UserName}','{$jsr}','{$Times}','{$nr}')";
$db->query($sql,0);
header("location:fabu.php");