function randomkeys($length)
{
    $pattern = '1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMNOPQRSTUVWXYZ';
    $key = '';
    for ($i = 0; $i < $length; $i++) {
        $key .= $pattern{mt_rand(0, 35)}; //生成php随机数
    }
    return $key;
}
echo randomkeys(24);