[RESOLVED] create unique random code each time

[vang]

hi,
i want to create a UNIQUE code and store in database every time a user register.
i've written some code below and wish to hear from the experts opinion, thanks.

do
{	// Create code
	$code = md5(uniqid(rand()));

// Check for duplicate code in database
$query = "SELECT * FROM users WHERE code = '$code'";
$result = mysql_query($query);

$count = mysql_num_rows($result);

if($count > 0)
{	// code exist in DB
	$row = mysqli_fetch_assoc($result);
	$code1 = $row["code"];
}
} while ($code == $code1);

[dagon]

UUID(), mysql_function, wont need to check if its a duplicate.

[Kudose]

Here is the PHP equivalent

function uuid(){
    return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
      mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff),
      mt_rand(0, 0x0fff) | 0x4000,
      mt_rand(0, 0x3fff) | 0x8000,
      mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff));
  }

[laserlight]

dagon wrote:

UUID(), mysql_function, wont need to check if its a duplicate.

To guarantee uniqueness, use a UNIQUE index on the column. Looking at the docs of UUID(), I would say that it does not guarantee uniqueness, even though you may need to rig the experiment to have a non-zero chance of a duplicate. However, if the code is really to appear random, then a cryptographic hash should be used on the output, in which case uniqueness would certainly not be guaranteed except by a UNIQUE index. Otherwise, given the use of timestamps in generating the UUID, it may be possible to guess the UUID within some small range, given sufficient knowledge of the system time and hardware.

Kudose wrote:

Here is the PHP equivalent

A good PHP "equivalent" would be to use [man]uniqid/man, possibly in conjunction with a cryptographic hash, which is what vang has done.