How to generate a random serial number

[eluser]Unknown[/eluser]
Hi,

This is what I want:

I'm generating a serial number and I need to make sure it doesn't exist already. So I generate the string, query the result in the table, if it doesn't exist I will record it, if it does I need to run the function again without having to refresh the page.

This is my code so far:

Code:

function generate_serial($length){
    
        $len=$length;
        $base='JKLMNOPQRS123456789';
        $max=strlen($base)-1;
        $rand_num='';
        mt_srand((double)microtime()*1000000);
        while (strlen($rand_num)<$len+1)
        $rand_num.=$base{mt_rand(0,$max)};
        
        $this->db->select("user");
        $this->db->from('serial');
        $this->db->where("user = '$rand_num'");
        $query = $this->db->get();
        
        if($query->num_rows() > 0)
        {
            // This is where I want to run again this same function to generate a new serial
            // $this->generate_serial($lenght); (I tried it but it doesn't seem to work this way!)
        }
        else
        {
            return $rand_num;
        }
    
    }

I have another function to insert the data into the table that is called from the controller.Thanks for your help,