Skrip dan Form CRUD untuk menambahkan data untuk PHP dan SQL

<?php
$koneksi = mysqli_connect("localhost","username_phpmyadmin","password_phpmyadmin","tabel_phpmyadmin");
//cek apakah tombol submit sudag ditekan atau belum
if( isset($_POST ["submit"]) ) {
//ambil  data dari tiap elemen form
$nidn = $_POST ["nidn"];
$nama_dosen = $_POST ["nama_dosen"];
$username = $_POST ["username"];
$password = $_POST ["password"];
$level = $_POST ["level"];
$ttl_dosen = $_POST ["ttl_dosen"];
$email_dosen = $_POST ["email_dosen"];
$hombase = $_POST ["hombase"];
$alamat_dosen = $_POST ["alamat_dosen"];
$hp = $_POST ["hp"];
//insert data mahasiswa
$query = "INSERT INTO dosen
VALUES
('', '$nidn', '$nama_dosen', '$username', '$password', '$level','$ttl_dosen','$email_dosen','$hombase','$alamat_dosen','$hp')
";
mysqli_query($koneksi, $query);
//cek apakah data berhasil di tambahkan
if( mysqli_affected_rows($koneksi) > 0 ) {
echo "Berhasi";
}else {
echo "gagal !";
echo "<br>";
echo mysqli_error($koneksi);
}
}

?>


<form action="" method="post">
<table>
<tr>
<td>NIDN</td>
<td><input type="text"name="nidn"></td>
</tr><tr>
<td>Nama Dosen</td>
<td><input type="text" name="nama_dosen"></td></tr>
<tr><td>Username</td><td><input type="text" name="username"></td></tr><tr>
<td>Password</td><td><input type="password" name="password"></td></tr><tr>
<td>Level</td><td><input type="text" name="level"></td></tr><tr>
<td>Tempat dan Tanggal Lahir</td><td><input type="text" name="ttl_dosen"></td></tr><tr>
<td>Email</td><td><input type="text" name="email_dosen"></td></tr><tr>
<td>Hombase</td><td><input type="text" name="hombase"></td></tr><tr>
<td>Alamat</td><td><input type="text" name="alamat_dosen"></td></tr><tr>
<td>HP</td><td><input type="text" name="hp"></td></tr>
<tr><td></td><td><button type="submit" name="submit">Simpan</button></td></tr>
</table>

</form>