因為MySQL默認的是MyISAM數據引擎，不支持事務也不支持外鍵，所以需要用到Innodb引擎，於是決定將mysql的默認引擎設置為innodb。
1 . 查看MySQL存儲引擎是用的哪個？登錄MySQL數據庫，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 |
+------------+---------+----------------------------------------------------------------+
說明目前默認的數據引擎是MyISAM，並且也支持InnoDB引擎。
2. 設置InnoDB為默認引擎：在配置文件my.cnf中的 [mysqld] 下面加入default-storage-engine=INNODB 一句，保存。
3. 重啟mysql服務器：mysqladmin -u root -p shutdown或者service mysqld restart 登錄mysql數據庫，在mysql>提示符下搞入show engines;命令。如果出現 InnoDB |DEFAULT，則表示我們 設置InnoDB為默認引擎成功。