gimana cara biar ada peringatan stok kurang dari permintaan keluar??

<?php
error_reporting(0);
error_reporting(E_ERROR | E_WARNING | E_PARSE);
error_reporting(E_ALL);
ini_set("error_reporting", E_ALL);
error_reporting(E_ALL & ~E_NOTICE);
?> 
<?php
	//kondisi jika data SES_USER masih kosong maka...
	if (isset($_SESSION['SES_USER'])=="") {
		//merefresh halaman ke index.php
		echo"<meta http-equiv='refresh' content='0;url=index.php'>";
	} else {	//jika SES_USER tidak kosong maka...
		include "koneksi.php";	//memanggil koneksi
?>
<?php
mysql_connect("localhost","root","");
mysql_select_db("dbstok");

$query = "select max(id_trans_klr) as Kode from brg_klr";
$hasil = mysql_query($query);
$data = mysql_fetch_array($hasil);
$kode = $data['Kode'];

$nourut = (int) substr($kode, 3, 3);
$nourut++;

//karakter tetap
$char = "OUT";
//mengatur 02 karakter berubah-ubah
$IdBaru = $char.sprintf("%03s",$nourut);
?>


<style type="text/css">
	caption {font-size:x-large}
</style>

<!-- link ke jQuery-1.4.4  -->
<link rel="stylesheet" href="jQuery-1.4.4/bundle/themes/base/jquery.ui.all.css">					
<script type="text/javascript" src="jQuery-1.4.4/jscript/jquery-1.4.4.min.js"></script>				
<script type="text/javascript" src="jQuery-1.4.4/jscript/jquery-ui-1.8.9.custom.min.js"></script>	
<script type="text/javascript" src="jQuery-1.4.4/bundle/ui/jquery.ui.datepicker.js"></script>		

<script> <!-- Javascript untuk fungsi kalender  -->
	$(function() {
		$( "#tanggal" ).datepicker({
			changeMonth: true,
			changeYear: true,
			dateFormat:'yy-mm-dd',
			yearRange: '1980:c+9'
		});	
	});
</script>
<style type="text/css">
a {
	text-decoration: none;
}
.inputnonaktif {
	background-color:#6F9;
}
</style>
<link href="thickbox/thickbox.css" rel="stylesheet" type="text/css" />
<script language="javascript" src="jquery/jquery-1.2.6.js"></script>
<script language="javascript" src="thickbox/thickbox.js"></script>

<script language="javascript">

var $jnoc = jQuery.noConflict();
	$jnoc(document).ready(function(){
	$jnoc("a.slick").click(function(){
	$jnoc(".active").removeClass("active");
	$jnoc(this).addClass("active");
	$jnoc(".content-slick").slideUp();
	var content_show = $jnoc(this).attr("title");
	$jnoc("#" +content_show).slideDown();
	});
	});


function selectbarang(kode_brg,nama_brg,kualitas,id_suplier){
	$jnoc('input[@name=kode_brg]').val(kode_brg);
	$jnoc('input[@name=nama_brg]').val(nama_brg);
  $jnoc('input[@name=kualitas]').val(kualitas);
  $jnoc('input[@name=id_suplier]').val(id_suplier);
  tb_remove(); // hilangkan dialog thickbox
}

function selectbrg_klr(kode_brg,nama_brg,kualitas,id_suplier){
	$jnoc('input[@name=kode_brg]').val(kode_brg);
	$jnoc('input[@name=nama_brg]').val(nama_brg);
  $jnoc('input[@name=kualitas]').val(kualitas);
  $jnoc('input[@name=id_suplier]').val(id_suplier);
  tb_remove(); // hilangkan dialog thickbox
}
</script>

<form name="frmSimpan" method="post" action="" enctype="multipart/form-data">
	<table width="450" align="center">
		<caption>INPUT BARANG KELUAR<br><br></caption>
        <tr>
			<td width="50%">ID Transaksi Keluar</td>
          	<td width="2%">:</td>
          	<td width="66%">
            <!-- echo $data['nim']; digunakan untuk menampilkan data dari field nim -->
            	<input type="text" name="id_trans_klr" maxlength="15" size="9" required="" value="<?php echo $IdBaru; ?>" readonly> 
                	
            </td>
        </tr>
        <tr>
			<td width="50%">Kode Barang</td>
          	<td width="2%">:</td>
          	<td width="66%">
        <input type="text" name="kode_brg" size="30" class="inputnonaktif" maxlength="8" required="" readonly id="kode_brg"><a href="cari_barang.php?width=400&amp;height=400" class="thickbox"><input type="submit" name="browse" id="browse3" value="Browse" /></a>
            *cari kode barang</tr></td>
            
            <tr>
			<td width="50%">Nama Barang</td>
          	<td width="2%">:</td>
          	<td width="66%">
            <input name="nama_brg" size="30" maxlength="30" required="" readonly>
            </td>
            </tr>
            <!--<input type="text" name="id_daftar" size="30" class="inputnonaktif" maxlength="8" required="" readonly id="id_daftar"><a href="cari_daftar.php?width=600&height=400" class="thickbox"><input type="submit" name="browse" id="browse3" value="Browse" /></a>
            *cari id pendaftaran</tr></td> -->
        <tr>
          	<td width="50%">Kualitas</td>
          	<td width="2%">:</td>
          	<td width="66%">
            <!-- echo $data['nama']; digunakan untuk menampilkan data dari field nama -->
            	<input name="kualitas" size="30" maxlength="30" required="" readonly>
                	
            </td>
        </tr>
        <tr>
          	<td width="50%">ID Suplier</td>
          	<td width="2%">:</td>
          	<td width="66%">
            <!-- echo $data['nama']; digunakan untuk menampilkan data dari field nama -->
            	<input name="id_suplier" size="30" maxlength="30" required="" readonly>
                	
            </td>
        </tr>
        <tr>
          	<td width="32%">Tanggal Keluar</td>
          	<td width="2%">:</td>
          	<td width="66%">
            	<input type="text" name="tgl_klr" id="tanggal"/>
			</td>
        </tr>
        <tr>
          	<td width="32%">Jumlah Keluar</td>
          	<td width="2%">:</td>
          	<td width="66%">
            	<input name="jml_klr" size="30" maxlength="30" required="" >
			</td>
        </tr>
        <tr>
          	<td width="32%">&nbsp;</td>
          	<td width="2%">&nbsp;</td>
          	<td width="66%">
            	<input name="btnSimpan" type="submit" value="Simpan">
                <!-- membuat link ke mahasiswa_tampil.php pada tombol Batal -->
          		<input name="btnBatal" type="reset" 
                	onclick="window.location.href='?page=barang_keluar&hal=1'" value="Batal" />
            </td>
        </tr>
	</table>
</form>


<?php


	//jika tombol Simpan di klik maka...
	if (isset($_POST['btnSimpan'])) {
		/*
		eksekusi query untuk memasukkan data pada tb_mahasiswa dengan field yang diisi
		nim,nama,jekel,alamat,sts_mhs
		
		".$_POST['txtNIM']." digunakan menampung data dari txtNIM
		... dst
		*/

		
		
		$sql_insert = "INSERT INTO brg_klr (id_trans_klr,tgl_klr,kode_brg,nama_brg,jml_klr,id_suplier) VALUES (
					'".$_POST['id_trans_klr']."',
					'".$_POST['tgl_klr']."',
					'".$_POST['kode_brg']."',	
					'".$_POST['nama_brg']."',
					'".$_POST['jml_klr']."',
					'".$_POST['id_suplier']."')";
		$query_insert = mysql_query($sql_insert) or die (mysql_error());
		
		//mengcopy file gambar ke lokasi yang ditentukan [folder=imgFoto]
		
		//jika proses penyimpanan berhasil maka...
		if ($query_insert) {
			//menampilkan pesan data berhasil disimpan
			echo"<script>alert('Simpan data berhasil !')</script>";
			//merefresh halaman ke mahasiswa_tampil.php
			echo "<meta http-equiv='refresh' content='0; url=?page=barang_keluar&hal=1'>";
		}
	}

	}//menutup kondisi jika SES_USER tidak kosong di atas

?>