<?PHP
    function get_random_ids_from_table(&$link, $table, $where = null, $length = -1)
    {
        $ids_r = mysqli_query($link, 'select id from `' . $table . '`' . ($where ? ' where ' . $where : ''));
        if(!$ids_r)
        {
            return array();
        }

        $count = mysqli_num_rows($ids_r);

        if(!$count)
        {
            return array();
        }

        $ids = array();
        if($length < 1 || $length > $count)
        {
            while($id = mysqli_fetch_assoc($ids_r))
            {
                $ids[] = $id['id'];
            }
            shuffle($ids);
        }
        else
        {
            foreach(array_rand(range(0, $count - 1), $length) as $offset)
            {
                mysqli_data_seek($ids_r, $offset);
                $id = mysqli_fetch_assoc($ids_r);
                $ids[] = $id['id'];
            }
        }

        mysqli_free_result($ids_r);

        return $ids;
    }