因为MySQL默认的是MyISAM数据引擎，不支持事务也不支持外键，所以需要用到Innodb引擎，于是决定将mysql的默认引擎设置为innodb。
1 . 查看MySQL存储引擎是用的哪个？登录MySQL数据库，在mysql>提示符下搞入show engines;命令。
+------------+---------+----------------------------------------------------------------+
| Engine | Support | Comment |
+------------+---------+----------------------------------------------------------------+
| MyISAM | DEFAULT | Default engine as of MySQL 3.23 with great performance |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables |
| InnoDB | YES | Supports transactions, row-level locking, and foreign keys |
| BerkeleyDB | YES | Supports transactions and page-level locking |
| BLACKHOLE | NO | /dev/null storage engine (anything you write to it disappears) |
| EXAMPLE | NO | Example storage engine |
| ARCHIVE | NO | Archive storage engine |
| CSV | NO | CSV storage engine |
| ndbcluster | NO | Clustered, fault-tolerant, memory-based tables |
| FEDERATED | NO | Federated MySQL storage engine |
| MRG_MYISAM | YES | Collection of identical MyISAM tables |
| ISAM | NO | Obsolete storage engine |
+------------+---------+----------------------------------------------------------------+
说明目前默认的数据引擎是MyISAM，并且也支持InnoDB引擎。
2. 设置InnoDB为默认引擎：在配置文件my.cnf中的 [mysqld] 下面加入default-storage-engine=INNODB 一句，保存。
3. 重启mysql服务器：mysqladmin -u root -p shutdown或者service mysqld restart 登录mysql数据库，在mysql>提示符下搞入show engines;命令。如果出现 InnoDB |DEFAULT，则表示我们 设置InnoDB为默认引擎成功。