其实是个很简单的操作，但是忽然有人问我就是想不起来，暂且做个笔记在这里。
mysql> create table test2(id int(2) AUTO_INCREMENT,name varchar(10),primary key(id));
Query OK, 0 rows affected (0.03 sec)
mysql> insert into test2 values(null,'a'),(null,'b'),(null,'c');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from test2;
+----+------+
| id | name |
+----+------+
| 1 | a |
| 2 | b |
| 3 | c |
+----+------+
3 rows in set (0.00 sec)
mysql> delete from test2 where id in (2,3);
Query OK, 2 rows affected (0.00 sec)
mysql> select * from test2;
+----+------+
| id | name |
+----+------+
| 1 | a |
+----+------+
1 row in set (0.00 sec)
mysql> insert into test2 values(null,'d');
Query OK, 1 row affected (0.00 sec)
mysql> select * from test2;
+----+------+
| id | name |
+----+------+
| 1 | a |
| 4 | d |
+----+------+
2 rows in set (0.00 sec)
mysql> delete from test2 where id = 4;
Query OK, 1 row affected (0.00 sec)
mysql> alter table test2 AUTO_INCREMENT=2;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> insert into test2 values(null,'f');
Query OK, 1 row affected (0.00 sec)
mysql> select * from test2;
+----+------+
| id | name |
+----+------+
| 1 | a |
| 2 | f |
+----+------+
2 rows in set (0.00 sec)
