Código PHP:
<select name="seleccion">
<?php
include('../php/includes/classDB.php');
include('conxDB.php');
$db = new DB($host,$datab,$user,$pass);
$codigo = $db->SelectCodigo();
foreach ($codigo as $value)
{
?><option value="<?php echo $value; ?>"><?php echo $value; ?></option><?php
}
?>
</select>
Código PHP:
$codigo = $_POST['seleccion'];