I can\'t imagine for myself a good answer for this, so I thought of asking it here. In my mind, I\'m always wondering what will happen if the AUTO INCREMENT PRIMARY ID
Once Autoincrement hit the limit for the field size, INSERTs will generate an error.
In practical you will get the following type of error:
ERROR 1467 (HY000): Failed to read auto-increment value from storage engine
For more info visit:
http://dev.mysql.com/doc/refman/5.1/en/example-auto-increment.html