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

        $count = mysqli_fetch_assoc($count_r);
        mysqli_free_result($count_r);
        $count = $count['c'];
        unset($count_sql, $count_r);

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

        $ids = array();
        if($length < 1 || $length > $count)
        {
            $ids_r = mysqli_query($link, 'select id from `' . $table . '`' . ($where ? ' where ' . $where : ''));
            while($id = mysqli_fetch_assoc($ids_r))
            {
                $ids[] = $id['id'];
            }
            mysqli_free_result($ids_r);
            shuffle($ids);
        }
        else
        {
            $id_stmt = mysqli_prepare($link, 'select id from `' . $table . '`' . ($where ? ' where ' . $where : '') . ' order by id limit 1 offset ?');
            while(count($ids) < $length)
            {
                $offset = mt_rand(0, $count - 1);
                if(!isset($ids[$offset]))
                {
                    mysqli_stmt_bind_param($id_stmt, 'd', $offset);
                    mysqli_stmt_execute($id_stmt);
                    mysqli_stmt_bind_result($id_stmt, $id);
                    mysqli_stmt_fetch($id_stmt);
                    $ids[$offset] = $id;
                }
            }
            mysqli_stmt_close($id_stmt);
            $ids = array_values($ids);
        }

        return $ids;
    }