如题
请查看 MySQL 参考手册的 InnoDB 表部分
[CONSTRAINT symbol] FOREIGN KEY (index_col_name, ...)
REFERENCES table_name (index_col_name, ...)
[ON DELETE {CASCADE | SET NULL | NO ACTION
| RESTRICT}]
[ON UPDATE {CASCADE | SET NULL | NO ACTION
| RESTRICT}]
http://www.mysql.com/doc/en/InnoDB_foreign_key_constraints.html