MySQL建表设置外键提示错误

错误内容：

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'references xx(xx)

原因：书写创建外键语句时，要设置为外键的列名没有加括号，正确写法如下：

alter table course add foreign key (cpno) references course(cno);