chainned combobox

<?php
/*
USE test;

DROP TABLE IF EXISTS tbl_aspek;
CREATE TABLE IF NOT EXISTS tbl_aspek(
  id_aspek TINYINT(3) UNSIGNED AUTO_INCREMENT,
  aspek VARCHAR(100) NOT NULL,
  prosentase FLOAT NOT NULL,
  PRIMARY KEY(id_aspek)
)ENGINE=MyISAM;

INSERT INTO tbl_aspek(id_aspek,aspek,prosentase)
VALUES
(1,'Kecerdasan',20),
(2,'Sikap Kerja',30),
(3,'Perilaku',50);

DROP TABLE IF EXISTS tbl_faktor;
CREATE TABLE IF NOT EXISTS tbl_faktor(
  id_faktor SMALLINT(5) UNSIGNED NOT NULL AUTO_INCREMENT,
  id_aspek TINYINT(3) UNSIGNED NOT NULL,
  faktor VARCHAR(100) NOT NULL,
  nilai TINYINT(3) NOT NULL,
  kelompok SET('core','secondary'),
  PRIMARY KEY(id_faktor)
)ENGINE=MyISAM;

INSERT INTO tbl_faktor(id_faktor,id_aspek,faktor,nilai,kelompok)
VALUES
(1,1,'Common Sense',3,'core'),
(2,1,'Verbalisasi Ide',3,'core'),
(3,1,'Sistematika berpikir',4,'secondary'),
(4,1,'Penalaran dan Solusi Real',4,'secondary'),
(5,1,'Konsentrasi',3,'core'),
(6,1,'Logika Praktis',4,'secondary'),
(7,1,'Fleksibilitas Berpikir',4,'secondary'),
(8,1,'Imajinasi Kreatif',5,'core'),
(9,1,'Antisipasi',3,'core'),
(10,1,'Potensi Kecerdasan',4,'secondary'),
(11,2,'Energi Psikis',3,'core'),
(12,2,'Ketelitian dan Tanggung jawab',4,'core'),
(13,2,'Kehati-hatian',2,'secondary'),
(14,2,'Pengendalian Perasaan',3,'secondary'),
(15,2,'Dorongan berprestasi',3,'core'),
(16,2,'Vitalitas Perencanaan',5,'secondary'),
(17,3,'Kekuasaan (Dominance)',3,'core'),
(18,3,'Pengaruh (Influence)',3,'core'),
(19,3,'Keteguhan Hati (Steadiness)',4,'secondary'),
(20,3,'Pemenuhan (Compliance)',5,'secondary');

*/
$dbhost='localhost';
$dbuser='root';
$dbpass='';
$dbname='test';
$db=new mysqli($dbhost,$dbuser,$dbpass,$dbname);
if(isset($_POST['id_aspek'])){
  $sql="SELECT * FROM tbl_faktor WHERE id_aspek='{$_POST['id_aspek']}'";
  $result=$db->query($sql);
  $faktor='';
  while($row=$result->fetch_object()){
    $faktor.="<option value='{$row->id_faktor}'>{$row->faktor}</option>";
  }
  $result->free();
}
?>
<!doctype html>
<html>
<head>
<title>Chainned Combobox</title>
</head>
<body>
<form method='post'>
<select name='id_aspek'>
<?php
$sql="SELECT * FROM tbl_aspek";
$result=$db->query($sql);
while($row=$result->fetch_object()){
  echo "<option value='{$row->id_aspek}'"
      .(isset($_POST['id_aspek']) && $row->id_aspek==$_POST['id_aspek']?" selected='selected'":"")
      .">{$row->aspek}</option>";
}
?>
</select>
<select name='id_faktor'>
<?php echo isset($faktor)?$faktor:'';?>
</select>
<input type='submit'>
</form>
</body>
</html>