The difficulty in random generation is how to avoid collisions. Some people say to use mechanisms such as md5 and GUID. Of course you can, but as an account, it looks messy, and the number of generated digits is too long.

This method only needs to solve concurrent collisions within 1 second, because the fixed head uses unixtime time, which is accurate to the second. If it exceeds 1 second, the time of this head must have changed. At the same time, this method can also generate random order numbers for users.

The test condition is to use a loop to create 10,000 random accounts (millisecond level), with 0 collisions, and 100,000 accounts with approximately 0-3 collisions. There should be no Internet company that would create so many accounts at the same time in an instant, so it is enough to handle a scale of billions of PV.

// Automatically generate random usernames

// Test, create 10,000 random accounts in a loop, 0 collisions, 100,000 about 0-3 collisions, enough to cope with billions of PV in the future

private function genUserNumber()
{
    $chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $username = "";
    for ( $i = 0; $i < 6; $i++ )
    {
        $username .= $chars[mt_rand(0, strlen($chars))];
    }
    return strtoupper(base_convert(time() - 1420070400, 10, 36)).$username;
}