php突然无法删除表里的数据，求助！！
<html>
<body>
<?php
require_once('connect.php');
$serial= $_POST['serial'];
$type=$_POST['type'];
$name=$_POST['name'];
$contact=$_POST['contact'];
$time=$_POST["time"];
echo $serial;
echo $type;
echo $name;
echo $contact;
echo $time;
$modifymysql="update work1 set job=$job where serial=$serial";
mysql_query($modifymysql);
?>
</body>
</html>
输出是正常的，但是当修改时就出现错误
Notice: Undefined variable: job in D:\wampserver\wamp\www\modify_check.php on line 15
