Problème php ajax

<div class="wrap">
  <h1>PHP jQuery Ajax Live Comment System</h1>
 <?php
  // retrive post
  include('config.php');
  include ('function.php');
  dbConnect();
  
  $query = mysql_query(
   'SELECT *
   FROM post
   WHERE post_id = 1');
  $row = mysql_fetch_array($query);
 ?>
  <div class="post">
   <h2 align="center"><?php echo $row['post_title']?></h2>
   <p><?php echo $row['post_body']?></p>
  </div>

 <?php
  // retrive comments with post id
  $comment_query = mysql_query(
   'SELECT *
   FROM comment
   WHERE post_id = 1');
   
 ?>

  <h2>Comments.....</h2>
  <div class="comment-block">
  <?php while($comment = mysql_fetch_array($comment_query)): ?>
   <div class="comment-item">
    <div class="comment-avatar">
     <img src="<?php echo avatar($comment['mail']) ?>" alt="avatar">
    </div>
    <div class="comment-post">
     <h3><?php echo $comment['name'] ?> <span>said....</span></h3>
     <p><?php echo $comment['comment']?></p>
    </div>
   </div>
  <?php endwhile?>
  </div>

  <h2>Tell Us How You Like Our Post..</h2>
  <!--comment form -->
  <form id="form" method="post">
   <!-- need to supply post id with hidden fild -->
   <input type="hidden" name="postid" value="<?php echo $row['post_id']?>">
   <label>
    <span>Name *</span>
    <input type="text" name="name" id="comment-name" placeholder="Your name here...." required autocomplete="off">
   </label>
   <label>
    <span>Email *</span>
    <input type="email" name="mail" id="comment-mail" placeholder="Your mail here....We Will Not Publish Your Email" required autocomplete="off">
   </label>
   <label>
    <span>Your comment *</span>
    <textarea name="comment" id="comment" cols="30" rows="10" placeholder="Type your comment here....Max Length 300 words" maxlength="300" required></textarea>
   </label>
   <input type="submit" id="submit" value="Submit Comment">
  </form>
 </div>