刷新时生成10位唯一编号

I am new to PHP and want to generate unique 10 digits number for my SKU Number. I tried using a date with IP address and got a unique value first time. But after a refresh or saving product data I still have that same SKU number. Any Help?? My code is:

    <?php
     if(!empty($_POST)) {
      .....my code......   
      }

      else{
       $stamp = date("Ymdhis");
       $ip = $_SERVER['REMOTE_ADDR'];
       $sku = "$stamp-$ip";
       $sku = str_replace(".", "", "$sku");
       $sku = str_replace("-", "", "$sku");
       $sku = str_replace(":", "", "$sku");
       $sku = substr($sku, 0,10);
       }
       ?>

Here's a quick random-string-generator I wrote:

function generateRandomString($alpha = true, $nums = true, $usetime = false, $string = '', $length = 120) {
$alpha = ($alpha == true) ? 'abcdefghijklmnopqrstuvwxyz' : '';
$nums = ($nums == true) ? '1234567890' : '';

if ($alpha == true || $nums == true || !empty($string)) {
    if ($alpha == true) {
        $alpha = $alpha;
        $alpha .= strtoupper($alpha);
    } 
}
$randomstring = '';
$totallength = $length;
    for ($na = 0; $na < $totallength; $na++) {
            $var = (bool)rand(0,1);
            if ($var == 1 && $alpha == true) {
                $randomstring .= $alpha[(rand() % mb_strlen($alpha))];
            } else {
                $randomstring .= $nums[(rand() % mb_strlen($nums))];
            }
    }
if ($usetime == true) {
    $randomstring = $randomstring.time();
}
return($randomstring);
} // end generateRandomString

You can use it like this for what you need:

$SKU = generateRandomString(false, true, false, '', 10);

you could use this $sku = rand(1000000000,9999999999) this php function will generate a random no. every time

Why not use the date to create a 10 digit unique number? year (4) + month with leading zero (2) + day with leading zero (2) + seconds with leading zero (2) = 10 digits

<?php
echo date("Ymds");
?>

Yall overcomplicating.

Use an existing library like random_compat (This library can generate strong random numbers and cryptographically secure random numbers.). https://github.com/ircmaxell/random_compat/blob/master/lib/random.php

Example (your case):

$random = new \PHP\Random(true);
echo $random->token(10, '0123456789');