现在来解释下：
start transaction;
就是开始事务追踪的命令
开始前一定记得写
然后
commit;
这个的意思是说确认提交，执行这个命令就不能rollback了，相当于执行完毕。
最后
rollback;
这个命令很简单，回滚到start transaction时候的状态
现在举例
mysql> select * from useraccount ;
+-----------+--------+-------------+
| AccountID | userID | AccountName |
+-----------+--------+-------------+
| 1 | 2 | zhifubao |
+-----------+--------+-------------+
1 row in set (0.00 sec)
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> update useraccount set userID = 1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from useraccount;
+-----------+--------+-------------+
| AccountID | userID | AccountName |
+-----------+--------+-------------+
| 1 | 1 | zhifubao |
+-----------+--------+-------------+
1 row in set (0.00 sec)
mysql> rollback; (这里假如不想回滚就用commit;就可以完成了）
Query OK, 0 rows affected (0.28 sec)
mysql> select * from useraccount;
+-----------+--------+-------------+
| AccountID | userID | AccountName |
+-----------+--------+-------------+
| 1 | 2 | zhifubao |
+-----------+--------+-------------+
1 row in set (0.00 sec)
