mysql 主键自增

ERROR 1049 (42000): Unknown database 'user'

mysql> alter table user modify Id integer auto_increment;

Query OK, 0 rows affected (0.06 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table user modify Id integer default '0';

Query OK, 0 rows affected (0.06 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table user modify Id integer auto_increment;

Query OK, 0 rows affected (0.06 sec)

Records: 0  Duplicates: 0  Warnings: 0

mysql> show table user

    -> ;

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 'user' at line 1

mysql> DESCRIBE user ;

+-------+--------------+------+-----+---------+----------------+

| Field | Type         | Null | Key | Default | Extra          |

+-------+--------------+------+-----+---------+----------------+

| Id    | int(11)      | NO   | PRI | NULL    | auto_increment |

| name  | varchar(200) | NO   |     | NULL    |                |

| psd   | varchar(200) | NO   |     | NULL    |                |

+-------+--------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)