以下是两次失败的尝试：

mysql> alter table shared_videos add column `id` int(10) unsigned AUTO_INCREMENT;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
mysql> alter table shared_videos add column `id` int(10) unsigned primary AUTO_INCREMENT;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AUTO_INCREMENT' at line 1