Stop resubmit on form

I have a simple form on my site that allows users to add comments on photos. However, the form doenst use ajax (like facebook). Instead, it submits the开发者_如何学Python form and refreshes the page. This is fine however, if a user reloads the page, there is an alert that he/she will resubmit the data resulting in two of the same comments. Id like to remove this resubmit without sending the user to a confirmation page. Thanks.

Here is my form:

<form name='form' action='index.php' method='POST'>
<input type='text' name='comment'>
<input type='submit' value='submit' name='submit'>

PHP:

if (isset($_POST['submit'])){

        $comment=$_POST[comment];
        $time=time();
             $id=$_GET['id'];
         $put=mysql_query("INSERT INTO comments VALUES ('','$user','$time','$comment','$id')");

Is your PHP script simply re-rendering the page in response to a form post? The standard way to get the behavior you describe is that it should either return a HTTP status of 204 (No content) or 303 (see other, with a redirect to the page you want to show).