PDO使用回调函数处理查询记录

$driver_options = array(
    PDO::ATTR_PERSISTENT => true
);
$db = new PDO('mysql:host=localhost;dbname=test', 'root', '123456', $driver_options);
   
$stmt = $db->query("SELECT username,password FROM members LIMIT 5");
   
$result = $stmt->fetchAll(PDO::FETCH_FUNC, 'callback_function');
   
var_dump($result);
   
function callback_function($username, $password)
{
    $return = array();
    $return['username'] = strtoupper($username);
    $return['password'] = $password;
    return $return;
}