public function getLimit($sql, $page, $num = 0, $params = array(), $next_page = false)
    {
        $num = (int)$num;
        $sql .= ' limit :limit_from,:limit';

        if ($next_page && $num) {
            $limit_from = ($page - 1) * ($num - 1);
        } else {
            $limit_from = ($page - 1) * $num;
        }

        $ret = $this->getAll($sql, array_merge($params, array('limit' => $num, 'limit_from' => $limit_from)));
        return $ret;
    }