Listbox PHP value dari MYSQL

<?php
$koneksi_db = mysql_connect("localhost", "root", ""); //membuka koneksi ke database
mysql_select_db("db_hclab", $koneksi_db);  //proses masuk ke database
$sql = "
SELECT
  `tbl_getdata`.`instrument_id`
FROM
  `tbl_getdata`
GROUP BY
  `tbl_getdata`.`instrument_id`
";
$query = mysql_query($sql);
?>
    <select class="form-control" name="id_kategori">
        <option value=""></option>
<?php
    while($hasil = mysql_fetch_array($query)){
?>
      <option value="<?php echo $hasil["instrument_id"];?>"><?php echo $hasil["instrument_id"];?></option>
<?php
}
?>
</select>