第一个代码能运行出结果，第二个不能出结果，想知道第二个怎么做才对？要最优关系代数式对应的SQL语句
第一个代码
select t_name,course_name,course_score
from teacher
inner join teaching
on teaching.t_no=teacher.t__no
inner join course
on teaching.course_no=course.course_no
where teacher.t_sex='男' and course.course_score='6'
结果
第二个代码
select r1.t_name,r2.course_name,r2.course_score
from(select t__no,t_sex,t_name
from teacher
where t_sex='男')as r1
inner join teaching
on teaching.t_no=r1.t__no
inner join(select *
from course
where course_score='6')as r2
on teaching.course_no=r2.course_score
结果
