ci4 data table server side with hermawan library change to raw sql

How to change my code get data table from builder method to raw sql in ci4 :

Original code :

$db = db_connect();
    $builder = $db->table('customers')->select('firstName, lastName, phone, address, city, 
               country');
    return DataTable::of($builder)
        ->addNumbering()
        ->toJson();

I tried change to code below but i get an error :

$db = ConfigDatabase::connect();
    $sql = "SELECT firstName, lastName, phone, `address`, city, country FROM customers";
    $data = $db->query($sql)->getResult();

    return DataTable::of($data)
        ->addNumbering()
        ->toJson();

Thank you.