Membuat Tampilan awal

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<div class="container mb-5">

<h2 align="center" style="margin: 60px 10px 10px 10px;">Combobox Bertingkat Daerah Indonesia</h2><hr>

<div class="row">

<div class="col-sm-6">

<div class="form-group">

<label>Provinsi</label>

<select class="form-control" name="provinsi" id="provinsi">

<option value=""> Pilih Provinsi</option>

</select>

</div>

<div class="form-group">

<label>Kabupaten</label>

<select class="form-control" name="kabupaten" id="kabupaten">

<option value=""></option>

</select>

</div>

<div class="form-group">

<label>Kecamatan</label>

<select class="form-control" name="kecamatan" id="kecamatan">

<option value=""></option>

</select>

</div>

<div class="form-group">

<label>Kelurahan</label>

<select class="form-control" name="kelurahan" id="kelurahan">

<option value=""></option>

</select>

</div>

</div>

</div>

<hr>

</div>

<div class="navbar bg-dark fixed-bottom">

<div style="color: #fff;">© <?php echo date('Y'); ?> Copyright:

    <a href="https://dewankomputer.com/"> Dewan Komputer</a>

</div>

</div>

<script type="text/javascript">

  $(document).ready(function(){

        $.ajax({

            type: 'POST',

            url: "get_provinsi.php",

            cache: false, 

            success: function(msg){

              $("#provinsi").html(msg);

            }

        });

        $("#provinsi").change(function(){

        var provinsi = $("#provinsi").val();

            $.ajax({

              type: 'POST',

                url: "get_kabupaten.php",

                data: {provinsi: provinsi},

                cache: false,

                success: function(msg){

                  $("#kabupaten").html(msg);

                }

            });

        });

        $("#kabupaten").change(function(){

        var kabupaten = $("#kabupaten").val();

            $.ajax({

              type: 'POST',

                url: "get_kecamatan.php",

                data: {kabupaten: kabupaten},

                cache: false,

                success: function(msg){

                  $("#kecamatan").html(msg);

                }

            });

        });

        $("#kecamatan").change(function(){

        var kecamatan = $("#kecamatan").val();

            $.ajax({

              type: 'POST',

                url: "get_kelurahan.php",

                data: {kecamatan: kecamatan},

                cache: false,

                success: function(msg){

                  $("#kelurahan").html(msg);

                }

            });

        });

     });

</script>

Membuat Get Provinsi

<?php

include 'koneksi.php';

echo "<option value=''>Pilih Provinsi</option>";

$koneksi = mysqli_connect("localhost","root","","feeder-importer-master");

          $query = "SELECT * FROM data_wilayah WHERE id_level_wil = '1' ORDER BY id DESC";

          $tampil_select_prov = mysqli_query($koneksi, $query); ?>

          <?php while( $tampil_prov = mysqli_fetch_assoc($tampil_select_prov)) {

          echo "<option value='" . $tampil_prov['id_wil'] . "'>" . $tampil_prov['nm_wil'] . "</option>"; }

?>

Membuat get Kabupaten

<?php

include 'koneksi.php';

$provinsi = $_POST['provinsi'];

echo "<option value=''>Pilih Kabupaten</option>";

echo "$provinsi";

$query = "SELECT * FROM data_wilayah WHERE id_induk_wilayah = '$provinsi' ORDER BY id DESC";

$tampil_select_prov = mysqli_query($koneksi, $query);

?>

<?php while( $tampil_prov = mysqli_fetch_assoc($tampil_select_prov)) : ?>

<option value="<?=$tampil_prov['id_wil']?>" ><?php echo $tampil_prov['nm_wil'] ?></option>

<?php endwhile ?>

Membuat Get Kecamatan

<?php

include 'koneksi.php';

$kecamatan = $_POST['kabupaten'];

echo "<option value=''>Pilih Kecamatan</option>";

echo "$provinsi";

$query = "SELECT * FROM data_wilayah WHERE id_induk_wilayah = '$kecamatan' ORDER BY id DESC";

$tampil_select_prov = mysqli_query($koneksi, $query);

?>

<?php while( $tampil_prov = mysqli_fetch_assoc($tampil_select_prov)) : ?>

<option value="<?=$tampil_prov['id_wil']?>" ><?php echo $tampil_prov['nm_wil'] ?></option>

<?php endwhile ?>