《数据库》 错误 ~1248 - Every derived table must have its own alias~

解决问题：“显示Comp. Sci. 系全部学生以及他们在2009年春季选修课的全部课程端的列表”

(1)错误源头：

select * from (select * from student where dept_name='Comp. Sci.')
     natural  left outer join            //左外链接
    (select * from takes where semester='Spring' and year=2009);

错误缘由：
1248 - Every derived table must have its own alias
//这句话的意思是说每一个派生出来的表都必须有一个本身的别名
//通常在多表查询时，会出现此错误。

(2)改正：
select * from (select * from student where dept_name='Comp. Sci.') as a
     natural left outer join
    (select * from takes where semester='Spring' and year=2009) as b;

 

推展：natural  right outer join  //右外链接（与左外链接相对称）

        natural full outer join      // 全外链接

        natural join                   //天然链接