未定义的索引向导，第3行和第4行的stu_name

Question

我试图仅借助JQuery的设置间隔和加载功能来刷新div。正在与数据库一起获取数据。我希望它重新加载，因为这是聊天门户

我试图在#chat中加载

chat1.php代码：

<?php
include('db.php');
  $ment=$_GET['mentor_name'];
  $stu=$_GET['stu'];
?>


<?php
if(isset($_POST['stu_send'])){
  $msg_student=$_POST['msg_student'];
  $sqls=mysqli_query($con,"insert into chats (student_email,mentor_email,content,sender_id) values ('$stu','$ment','$msg_student','$stu')");
echo '<a href="chat1.php?stu=<?php echo $stu; ?> & mentor=<?php echo $ment; ?>"></a>';
}
 $chat=mysqli_query($con,"select content,sender_id,c_date from chats where student_email='$stu' AND mentor_email='$ment'");
  while($row_con=mysqli_fetch_array($chat)){
    $sender_id=$row_con['sender_id'];
    $cont=$row_con['content'];
    $c_date=$row_con['c_date'];

 echo $sender_id.": "; 
 echo $cont . "<br/>";
 echo $c_date;
// echo date("h:i:sa");
// echo date("Y/m/d");
  echo "<hr>";
 }
 ?>

刷新代码：

setInterval(refreshMessages, 1000);
function refreshMessages() {
  $.ajax({
    url: 'chat1-1.php',
    type: 'GET',
    dataType: 'html',
    success: function(data) {
      $('#chat').html(data); // data came back ok, so display it
    },
    error: function() {
      $('#chat').prepend('Error retrieving new messages..');
    }
  });
}