how to build jquery messages notification with php and mysq

                                    <script>

$(document).ready(function(){

// updating the view with notifications using ajax

function load_unseen_notification(view = '')

{

 $.ajax({

  url:"fetch.php",
  method:"POST",
  data:{view:view},
  dataType:"json",
  success:function(data)

  {

   $('.dropdown-menu').html(data.notification);

   if(data.unseen_notification > 0)
   {
    $('.count').html(data.unseen_notification);
   }

  }

 });

}

load_unseen_notification();

// submit form and get new records

$('#comment_form').on('submit', function(event){
 event.preventDefault();

 if($('#subject').val() != '' && $('#comment').val() != '')

 {

  var form_data = $(this).serialize();

  $.ajax({

   url:"insert.php",
   method:"POST",
   data:form_data,
   success:function(data)

   {

    $('#comment_form')[0].reset();
    load_unseen_notification();

   }

  });

 }

 else

 {
  alert("Both Fields are Required");
 }

});

// load new notifications

$(document).on('click', '.dropdown-toggle', function(){

 $('.count').html('');

 load_unseen_notification('yes');

});

setInterval(function(){

 load_unseen_notification();;

}, 5000);

});

</script>

                                    <script type="text/javascript">

$(document).ready(function(){
$("#datacount").load("select.php");
setInterval(function(){
$("#datacount").load('select.php')
}, 20000);
 });

</script>

                                    <li class="dropdown dropdown-extended dropdown-notification dropdown-dark" id="header_notification_bar">

                                <a href="#" class="dropdown-toggle" data-toggle="dropdown" data-hover="dropdown" data-close-others="true">
                                    <i class="icon-bell"></i>
                                    <span class="badge badge-success"><div id="datacount"></div></span> </span>
                                </a>
                                <ul class="dropdown-menu" >
                                    <li class="external">
                                        <h3>
                                            <span class="bold">12 pending</span> notifications</h3>
                                        <a href="page_user_profile_1.html">view all</a>
                                    </li>
                                    <li>
                                        <ul class="dropdown-menu-list scroller" style="height: 250px;" data-handle-color="#637283">
                                            <li>
                                                <a href="javascript:;">
                                                    <span class="time">just now</span>
                                                    <span class="details">
                                                        <span class="label label-sm label-icon label-success">
                                                            <i class="fa fa-plus"></i>
                                                        </span> New user registered. </span>
                                                </a>
                                            </li>

                                        </ul>
                                    </li>
                                </ul>
                            </li>

                                    <?php

include('connect.php');

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

// $con = mysqli_connect("localhost", "root", "", "notif");

if($_POST["view"] != '')

{
   $update_query = "UPDATE comments SET comment_status = 1 WHERE comment_status=0";
   mysqli_query($con, $update_query);
}

$query = "SELECT * FROM comments ORDER BY comment_id DESC LIMIT 5";
$result = mysqli_query($con, $query);
$output = '';

if(mysqli_num_rows($result) > 0)
{

while($row = mysqli_fetch_array($result))

{

  $output .= '
  <li>
  <a href="#">
  <strong>'.$row["comment_subject"].'</strong><br />
  <small><em>'.$row["comment_text"].'</em></small>
  </a>
  </li>

  ';
}
}

else{
    $output .= '<li><a href="#" class="text-bold text-italic">No Noti Found</a></li>';
}

$status_query = "SELECT * FROM comments WHERE comment_status=0";
$result_query = mysqli_query($con, $status_query);
$count = mysqli_num_rows($result_query);

$data = array(
   'notification' => $output,
   'unseen_notification'  => $count
);

echo json_encode($data);
}
?>