All the answers posted are correct, but I think you are still better off to allow MySql's auto-number feature to manage your unique id key. Make sure you set the id field type to BIGINT.

Like I said before, gaps in the sequence do not matter. Auto-number's purpose is not to maintain a nice sequence of id's but rather to maintain a unique id.

As mentioned by another poster, you can always generate your own unique id within your code, and use that when inserting new records, but that increases the chance of hurting data integrity. Especially if you have a large application with multiple places in the code the table is inserted into. Database systems started implementing methods to manage unique ID's and relational integrity because it's too easy for us programmers to screw it up if we try to manage it in our code!