auto generate serial number in php code example

Example: php generate serial number

function GenerateSerial() {
  $chars = array(0,1,2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z');
  $sn = '';
  $max = count($chars)-1;
  for($i=0;$i<20;$i++){
   	$sn .= (!($i % 5) && $i ? '-' : '').$chars[rand(0, $max)];
  }
  return $sn;
}

$serial = GenerateSerial() ;

while (checkifSerialexist($dbh, $serial))
{
   $serial = GenerateSerial() ;
}

function checkifSerialexist ($dbh, $serial)
{
  $statement = $dbh->prepare("SELECT `id` FROM `table` WHERE `SN` = :existSN");
  $statement->bindParam(':existSN',  $serial, PDO::PARAM_STR); 
  $statement->execute();
  $statement->setFetchMode(PDO::FETCH_ASSOC);
  $result = $statement->fetchAll();

  return (count($result) > 0);   
}