MySQL 5.5 报错"ERROR 1075 (42000): Incorrect table definition"

--给表增加自增字段的时候报错

Mysql> desc t7;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(20) | YES  |     | NULL    |       |
| id    | int(4)      | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)