Membuat Combo berantai dalam satu database.

Simpan dalam dpl_data.php

<form method="POST" action="dkkn_tambah_simpan.php">

<tbody>
<tr> <input type="text" value="<?php echo $_GET['angkatan']; ?>" id="angkatan" name="angkatan" /></tr>

<tr><td>Nama DPL</td><td>:

<select name="nama" id="nama">
    <option value="">- Pilih Nama Dosen -</option>
   
    <!-- looping data nama -->
    <?php
    $sql_dosen="select * from tbdos";
    $q=$mysqli->query($sql_dosen);
    while($row_dosen=mysqli_fetch_array($q)){
   
    ?>
        <option value="<?php echo $row_dosen["nip"] ?>"><?php echo $row_dosen["nip"] ." - " . $row_dosen["nama"] ?></option>
   
    <?php
    }
    ?>
</select>

    &nbsp;&nbsp;&nbsp;<img src="loader.gif" width="10px" height="10px" id="imgLoad" style="display:none">
    <br>

<tr><td>NIK Dosen</td><td>: 
 <select name="kota" id="kota">
    <!-- hasil data dari cari_dosen.php akan ditampilkan disini ----------------------------------------------->
</select>


<tr><td>Type KKN</td><td>:
<select id="jenis" name ="jenis" />
<option value="Reguler 1" placeholder="Reguler I">Reguler 1
<option value="Reguler 2" placeholder="Reguler I">Reguler 2
<option value="Tematik" placeholder="Reguler I">Tematik
&nbsp;&nbsp;&nbsp;<img src="loader.gif" width="10px" height="10px" id="imgLoad" style="display:none">
</select>
</td></tr>

<tr><td>Tahun Akademik</td><td>:
<select id="tahun_akademik" name ="tahun_akademik" />
<?php include ("menu/listtakalender.php"); ?>
</select>
</td></tr>

<tr><td>Semester</td><td>:
<select  id="semester" name ="semester" />
<option placeholder="Pilih Semester">- Pilih Semester Ganjil/Genap
<option value="1" placeholder="">Ganjil
<option value="2" placeholder="">Genap
<option value="2" placeholder="">Antar Waktu
</select>
</td></tr>
</tbody>
</table>
<button type="submit" id="submit" class="btn btn-small btn-warning" ><a href="javascript:void(0)"></a><i class="icon-upload"></i> Simpan</button>

</form>



=============


Paling bawah ditambah script:
<script>
 
    $("#nama").change(function(){
 
        // variabel dari nilai combo box nama
        var nik = $("#nama").val();
     
        // tampilkan image load
        $("#imgLoad").show("");
     
        // mengirim dan mengambil data
        $.ajax({
            type: "POST",
            dataType: "html",
            url: "menu/cari_dosen.php",
            data: "prov="+nik,
            success: function(msg){
             
                // jika tidak ada data
                if(msg == ''){
                    alert('Tidak ada data Dose ');
                }
             
                // jika dapat mengambil data,, tampilkan di combo box kota
                else{
                    $("#kota").html(msg);                                                    
                }
             
                // hilangkan image load
                $("#imgLoad").hide();
            }
        });  
    });
</script>

Simpan dalam menu/cari_dosen.php
<?php
// server info
$server = 'localhost';
$user = 'root';
$pass = '';
$db = 'simpeg';

// connect to the database
$mysqli = new mysqli($server, $user, $pass, $db);

// show errors (remove this line if on a live site)
mysqli_report(MYSQLI_REPORT_ERROR);

?>  
<?php

 
    $sql_dosen1="select * from tbdos where nip='".$_POST["prov"]."'";
    $q=$mysqli->query($sql_dosen1);
    while($row_dosen1=mysqli_fetch_array($q)){
 
    ?>
        <option value="<?php echo $row_dosen1["nip"] ?>"><?php echo $row_dosen1["nip"] ?></option><br>
 
    <?php
    }
    ?>