public function run($sql, array $params = array())
    {
        $sth = $this->pdo->prepare($sql);

        foreach ($params as $key => $value) {
            $key = is_numeric($key) ? $key + 1 : ":$key";
            $sth->bindValue($key, $value);
        }

        $sth->execute($params);
        $this->executed[] = $sql;
        return $sth;
    }