用php编辑数据

Question

I edit my database on php, it said I success editing my data, but when I check on my sql database, It's not change yet ...

here is the code

<?php
$koneksi = mysql_connect("localhost", "root", "") or die("Gagal konek ke  server.");
mysql_select_db("kasatrian") or die("Gagal membuka database.");
$nis = isset($_GET['nis']) ? $_GET['nis'] :null;
$query = "select * from siswa where nis='$nis'";
$hasil = mysql_query($query, $koneksi) or die("Gagal melakukan query.");
$buff = mysql_fetch_array($hasil);
    mysql_close($koneksi);?>

<form name="form1" method="post" action="edit2.php">
<input type="hidden" name="nis" value="<?php echo $buff['nis']; ?>" />
<table>
<tr>
<td colspan=3><center><font size=5>EDIT DATA SISWA</font></center></td>
</tr>
<tr>
<td>Nama</td><td>:</td><td><input type="text" name="nama" value="<?php echo $buff['nama']; ?>"></td>
</tr>

<tr>
<td colspan=2></td>
<td colspan="3"><input type="submit" name="submit" value="Simpan" /></td>
</tr>
</table>
</form>
<p>Batal mengedit data. Kembali ke <a href="datasiswa.php">Data Siswa</a></p>
</tr>
</table>

and here is the edit process

<?php
$koneksi = mysql_connect("localhost", "root", "") or die("Gagal konek ke server.");

mysql_select_db("kasatrian") or die("Gagal membuka database.");

$nama = isset($_POST['nama']) ? $_POST['nama']: " ";

$query = mysql_query("update siswa set 
nama='$nama' where nis='$nis' ");

mysql_close($koneksi);

?>

<p>Data sudah ter-update. Silakan dicek di <a href="datasiswa.php">data siswa</a></p>

</body>

</html>

the code said it already save, but when I check my DB on SQL, nothing change.