Kode Autonumber

<?php
/*
DROP TABLE IF EXISTS alamat;
CREATE TABLE IF NOT EXISTS alamat(
    id INT(3) ZEROFILL AUTO_INCREMENT,
    tipe INT(1),
    nama VARCHAR(50),
    alamat VARCHAR(255),
    PRIMARY KEY (tipe,id)
) ENGINE=MyISAM;
*/
$dbhost='localhost';
$dbuser='root';
$dbpass='';
$dbname='test';
$db=new mysqli($dbhost,$dbuser,$dbpass,$dbname);
if(isset($_POST['nama'])){
    $sql="INSERT INTO alamat(tipe,nama,alamat) VALUES({$_POST['tipe']},'{$_POST['nama']}','{$_POST['alamat']}')";
    $result=$db->query($sql);
}
$sql="SELECT * FROM alamat ORDER BY tipe,id";
$result=$db->query($sql);
?>
<!DOCTYPE html>
<html>
<head>
    <title>Data Alamat</title>
</head>
<body>
<fieldset>
    <legend>Tambah Data</legend>
    <form method='post'>
        <table>
        <tr><td>Nama Perusahaan</td><td><input type='text' name='nama' required></td></tr>
        <tr><td>Alamat Perusahaan</td><td><input type='text' name='alamat' required></td></tr>
        <tr><td>Tipe Perusahaan</td><td>
            <select name='tipe' required>
                <option value='1'>Customer</option>
                <option value='2'>Vendor</option>
            </select>
        </td></tr>
        <tr><td colspan='2'><input type='submit' value='add'></td></tr>
        </table>
    </form>
</fieldset>
<fieldset>
    <legend>Daftar Alamat</legend>
    <?php
    if(!empty($result)) {
        if($result->num_rows>0){
            $code=array('1'=>array('CUS','Customer'),'2'=>array('VEN','Vendor')); //<-- kalo pengin dinamis buatin tabel tersendiri di db
            echo "<table>"
                ."<tr><th>Kode</th><th>Tipe</th><th>Nama</th><th>Alamat</th></tr>";
            while($r=$result->fetch_object()){
                echo "<tr><td>{$code[$r->tipe][0]}-{$r->id}</td><td>{$code[$r->tipe][1]}</td><td>{$r->nama}</td><td>{$r->alamat}</td></tr>";
            }
            echo "</table>";
        }
    }
    ?>
</fieldset>
</body>
</html>