[HELP] Input field tapi apabila filed kosong, tidak bisa tersimpan

Permisi suhu,, saya baru belajar php, minta bantuanya suhu
saya punya form inputan, dan rencana saya, apabila field dr salah satu tidak diisi, maka tidak bisa tersimpan ke database, dan muncul notif " Nama Harus Diisi / Form dll harus diisi " sperti itu suhu, 

berikut coding nya

kupon.php

<?php include 'header.php'; ?>



<h3><span class="glyphicon glyphicon-briefcase"></span>  Data Kupon Blonjo Bejo</h3>

<button style="margin-bottom:20px" data-toggle="modal" data-target="#myModal" class="btn btn-info col-md-2"><span class="glyphicon glyphicon-plus"></span>Tambah Data Kupon</button>

<br/>

<br/>





<?php 

$per_hal=10;

$jumlah_record=mysql_query("SELECT COUNT(*) from kupon");

$jum=mysql_result($jumlah_record, 0);

$halaman=ceil($jum / $per_hal);

$page = (isset($_GET['page'])) ? (int)$_GET['page'] : 1;

$start = ($page - 1) * $per_hal;

?>

<div class="col-md-12">

 <table class="col-md-2">

  <tr>

   <td>Jumlah Record</td>  

   <td><?php echo $jum; ?></td>

  </tr>

  <tr>

   <td>Jumlah Halaman</td> 

   <td><?php echo $halaman; ?></td>

  </tr>

 </table>

 <a style="margin-bottom:10px" href="lap_kupon.php" target="_blank" class="btn btn-default pull-right"><span class='glyphicon glyphicon-print'></span>  Cetak</a>

</div>

<form action="cari_act.php" method="get">

 

  <div class="input-group col-md-5 col-md-offset-7"> <span class="input-group-addon" id="basic-addon1"><span class="glyphicon glyphicon-search"></span></span> 

    <input type="text" class="form-control" placeholder="Cari Dengan No Kupon .." aria-describedby="basic-addon1" name="cari">

  </div>

</form>

<br/>

<table class="table table-hover">

 <tr>

  <th width="20" class="col-md-1">No</th>

  <th width="72" class="col-md-4">No Kupon</th>

  <th width="105" class="col-md-3">Nama Customer</th>

  <th width="30" class="col-md-1">NIK KTP/SIM</th>

  <th width="48" class="col-md-1">Alamat</th>

  <!-- <th class="col-md-1">Sisa</th>  -->

  <th width="110" class="col-md-3">Opsi</th>

 </tr>

 <?php 

 if(isset($_GET['cari'])){

  $cari=mysql_real_escape_string($_GET['cari']);

  $barang=mysql_query("select * from kupon where nokupon like '$cari' or namacustomer like '$cari'");

 }else{

  $barang=mysql_query("select * from kupon limit $start, $per_hal");

 }

 $no=1;

 while($b=mysql_fetch_array($barang)){



  ?>

  <tr>

   <td><?php echo $no++ ?></td>

   <td><?php echo $b['nokupon'] ?></td>

   <td><?php echo $b['namacustomer'] ?></td>

   <td><?php echo $b['nik'] ?></td>

   <td><?php echo $b['alamat'] ?></td>

   <td>

    <a href="det_kupon.php?id=<?php echo $b['id']; ?>" class="btn btn-info">Detail</a>

    <a href="edit_kupon.php?id=<?php echo $b['id']; ?>" class="btn btn-warning">Edit</a>

    <a>Hapus</a>

   </td>

  </tr>  

  <?php 

 }

 ?>

 <tr>

  

    <td colspan="4"> </td>

 <td>  </td>

    <td>  </td>

 </tr>

</table>

<ul class="pagination">   

   <?php 

   for($x=1;$x<=$halaman;$x++){

    ?>

    <li><a href=""><?php echo $x ?></a></li>

    <?php

   }

   ?>      

  </ul>

<!-- modal input -->

<div id="myModal" class="modal fade">

 <div class="modal-dialog">

  <div class="modal-content">

   <div class="modal-header">

    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>

    <h4 class="modal-title">Tambah Data Kupon</h4>

   </div>

   <div class="modal-body">

    <form method="post" action="tmb_kupon_act.php" >

     

     <div class="form-group form-group-lg has-feedback">

      <label>Nama Customer</label>

      <input name="namacustomer" type="text" class="form-control textbox" placeholder="Nama Customer ..">

      <i class="form-control-feedback"></i>

       <span class="text-warning" ></span>

     </div>

     <div class="form-group">

      <label>NIK KTP/SIM</label>

      <input name="nik" type="text" class="form-control" placeholder="NIK KTP/SIM ..">

     </div>

     <div class="form-group">

      <label>Alamat</label>

      <input name="alamat" type="text" class="form-control" placeholder="Alamat Cust ..">

     </div>

     <div class="form-group">

      <label>Nomor Telpon</label>

      <input name="notelp" type="text" class="form-control" placeholder="Nomor Telepon ..">

     </div>

     

      <div class="form-group">

       <label>Tanggal Pembelian </label>

       <input name="tgl_pembelian" type="text" class="form-control" id="tgl" autocomplete="off">

      </div>

      

      <div class="form-group">

         <label>Cara Pembayaran </label> 

                <select name="cara_pembayaran">

                            <option value="Tunai">Tunai</option>

                            <option value="EDC Mandiri">EDC Mandiri</option>

                            <option value="EDC Bank Lain">EDC Bank Lain</option>

                        </select>

</select>

          

    

     <p> </p>

     

        </div>

      

     <div 

      class="form-group">

      <label>Nama Toko</label>

      <input name="namatoko" type="text" class="form-control" placeholder="Nama Toko ..">

     </div>

     

     <div class="form-group">

      <label>No Kupon</label>

      <input name="nokupon" type="text" class="form-control" placeholder="No Kupon ..">

     </div>

     

     <div

     class="form-group">

     <strong>Nominal Belanja</strong> 

          <input name="nominalbelanja" type="int" class="form-control" id="txt1" >

          <strong>Jumlah 

          Kupon </strong> 

          <input  name="jumlahkupon" type="int" id="nominalbelanja" >

          <strong>Kupon</strong> 

            [removed]

     function sum() {

           var txtFirstNumberValue = document.getElementById('txt1').value;



           var result = parseInt(txtFirstNumberValue) / parseInt('50000');

           if (!isNaN(result)) {

            document.getElementById('nominalbelanja').value = result;

            }

      }

    [removed]

     </div>



     

     



     <div class="form-group">

      

          <label></label>

        </div>

     

         



    <div class="modal-footer">

     <button type="button" class="btn btn-default" data-dismiss="modal">Batal</button>

     <input type="submit" class="btn btn-primary" value="Simpan">

    </div>

   </form>

  </div>

 </div>

</div>



[removed]

  $(document).ready(function(){

   $("#tgl").datepicker({dateFormat : 'yy/mm/dd'});       

  });

 [removed]



<?php include 'footer.php';  ?>

tmb_kupon_act.php

<?php 

include 'config.php';



// menyimpan data kedalam variabel



$nokupon=$_POST['nokupon'];

$namacustomer=$_POST['namacustomer'];

$nik=$_POST['nik'];

$alamat=$_POST['alamat'];

$notelp=$_POST['notelp'];

$tgl_pembelian=$_POST['tgl_pembelian'];

$cara_pembayaran=$_POST['cara_pembayaran'];

$namatoko=$_POST['namatoko'];

$nominalbelanja=$_POST['nominalbelanja'];



// query SQL untuk insert data



mysql_query("insert into kupon values('','$nokupon','$namacustomer','$nik','$alamat','$notelp','$tgl_pembelian','$cara_pembayaran','$namatoko','$nominalbelanja')");

header("location:kupon.php");



 ?>

ini db, table dan field nya

Mohon bantuanya suhu,, terima kasih