如何为支持票证生成ID?

I am trying to generate support tickets for my website support option. I won't be using much features with the support system. I just want that the generated ticket ID numbers to not be repeated. What I tried gave me '0' two times in my database and single digits sometimes.

What I want is that whenever a new ticket is generated it should have consistent number of digits and never to repeat again.

The following is my code which I am using:

   $token = openssl_random_pseudo_bytes(16);
   $ticket = bin2hex($token);

Please guide me a better way.

What kind of database are you using?

Use auto-increment to create unique ID's for your tickets. MySql has an item about his here