--查询班级表、课程表、学生选课表、学生表、成绩表、15（3+2）计算班的期中成绩（qzcj）
--第一步选择表
select
from Class join Student
join StuCou
join Course
join achievement
--第二步定义列
on Class.ClassNo=student.ClassNo
on student.StuNo=stucou.StuNo
on stucou.CouNo=Course.CouNo
on StuCou.StuNo=achievement.StuNO
--第三步定义条件
select
from Class join Student
on Class.ClassNo=student.ClassNo
join StuCou
on student.StuNo=stucou.StuNo
join Course
on stucou.CouNo=Course.CouNo
join achievement
on StuCou.StuNo=achievement.StuNO
where Class.ClassName='2015(3+2)计算机'