php提交表单时提示“undefined index submit”

Question

数据是进入数据库了，为什么会提示这行？
include("conn.php");

if($_POST['submit']){

$sql="insert into message (id,user,title,content,lastdate) " .
"values ('','$_POST[user]','$_POST[title]','$_POST[content]',now())";
mysql_query($sql);
echo "<script language=\"javascript\">alert('添加成功');history.go(-1)</script>";

}
include("head.php");
?>

<form action="add.php" method="post" name="myform" onsubmit="return CheckPost();">
用户：<input type="text" size="10" name="user" /><br>
标题：<input type="text" name="title" /><br/>
内容：<textarea name="content" cols="60" rows="9"></textarea><br/>

<input type="submit" name="submit" value="发布留言"/>

</form>

Answer 1

代码有漏洞~想解决就贴
if(isset($_POST[submit])){
if($_POST[submit]){
......
}

}