解析mysql中的auto_increment的问题

mysql> select * from test1;
+----+-----------+
| id | name      |
+----+-----------+
|  1 | 陈兵辉    |
|  2 | chen      |
|  3 | chen      |
|  4 | chen      |
|  5 | chen      |
|  6 | chen      |
|  7 | chen      |
|  8 | chen      |
|  9 | chen      |
| 10 | chen      |
| 11 | chen      |
+----+-----------+
11 rows in set (0.00 sec)

mysql> delete from test1 where id in (10,11,9);
Query OK, 3 rows affected (0.03 sec)

mysql> show create table test1;
 CREATE TABLE `test1` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(10) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=<SPAN style="COLOR: #ff0000">12</SPAN> DEFAULT CHARSET=utf8 |
mysql> exit;
Bye
[root@fsailing1 ~]# service mysqld restart
停止 MySQL：                                               [确定]
启动 MySQL：                                               [确定]
[root@fsailing1 ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.0.95 Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show create table test1;
| CREATE TABLE `test1` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(10) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=<SPAN style="COLOR: #ff0000">9</SPAN> DEFAULT CHARSET=utf8 |

mysql> select last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|                0 |
+------------------+
1 row in set (0.00 sec)