How to auto suggest texts retrieved from Mysql Database in PHP

I have use following method to get autosuggest texts from mysql tables.

<div id="add_data_Modal" class="modal fade">
 <div class="modal-dialog">
  <div class="modal-content">
   <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal">&times;</button>
    <h4 class="modal-title">Issue a new Book</h4>
   </div>
   <div class="modal-body">
    <form method="post" id="insert_form">
    <label>Enter Book Name</label>
     <input type="text" name="book_name" id="book_name" class="form-control" />
     <br />
     <input type="submit" name="insert" id="insert" value="Insert" class="btn btn-success" />

    </form>
   </div>
   <div class="modal-footer">
    <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
   </div>
  </div>
 </div>
</div>

<div id="dataModal" class="modal fade">
 <div class="modal-dialog">
  <div class="modal-content">
   <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal">&times;</button>
    <h4 class="modal-title">Employee Details</h4>
   </div>
   <div class="modal-body" id="employee_detail">

   </div>
   <div class="modal-footer">
    <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
   </div>
  </div>
 </div>
</div>

<script type="text/javascript">
  $(function() {
     $( "#book_name" ).autocomplete({
       source: 'bookname-search.php',
     });
  });
</script>

But the issue is suggested texts are not showing on top of popup container but behind on it. Can someone help me to solve this issue?