Resultater fra data over flere sider

<?php
abstract class DAL {
    private $con;
    protected function __construct($constr, $un, $pw) {
        $this->con = new PDO($constr, $un, $pw);
        $this->con->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    }
    private function get($sqlstr, $parm) {
        $stmt = $this->con->prepare($sqlstr);
        foreach($parm as $parmkey => $parmval) {
            $stmt->bindValue($parmkey, $parmval, gettype($parmval) == "integer" ? PDO::PARAM_INT : PDO::PARAM_STR);
        }
        $stmt->execute();
        return $stmt->fetchAll();
    }
    public function get_all() {
        return $this->get('SELECT f1,f2 FROM t1', array());       
    }
    public function get_n($n) {
        return $this->get($this->get_select_n(), array(':n' => $n));       
    }
    protected abstract function get_select_n();
}

class MySQL_DAL extends DAL {
    public function __construct($host, $db, $un, $pw) {
        parent::__construct(sprintf('mysql:host=%s;dbname=%s', $host, $db), $un, $pw);
    }
    protected function get_select_n() {
        return 'SELECT f1,f2 FROM t1 ORDER BY f1 LIMIT :n';
    }
}

class SQLServer_DAL extends DAL {
    public function __construct($host, $db) {
        parent::__construct(sprintf('sqlsrv:server=%s;database=%s', $host, $db), '', '');
    }
    protected function get_select_n() {
        return 'SELECT f1,f2 FROM (SELECT f1,f2,ROW_NUMBER() OVER (ORDER BY f1) AS rownum FROM t1) x WHERE rownum <= :n';
    }
}

try {
   
    $dal1 = new MySQL_DAL('localhost', 'Test', 'root', '');
    $resall1 = $dal1->get_all();
    foreach($resall1 as $row) {
        echo $row['f1'] . ' ' . $row['f2'] . "\r\n";
    }
    $ressome1 = $dal1->get_n(2);
    foreach($ressome1 as $row) {
        echo $row['f1'] . ' ' . $row['f2'] . "\r\n";
    }
   
    $dal2 = new SQLServer_DAL('(local)', 'Test');
    $resall2 = $dal2->get_all();
    foreach($resall2 as $row) {
        echo $row['f1'] . ' ' . $row['f2'] . "\r\n";
    }
    $ressome2 = $dal2->get_n(2);
    foreach($ressome2 as $row) {
        echo $row['f1'] . ' ' . $row['f2'] . "\r\n";
    }
   
} catch (PDOException $ex) {
    die($ex->getMessage());
}

?>