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5.mysql知识内连接(内连接先连谁不讲究,但是什么表相邻是讲究的)

科牛 2022-02-22 阅读 111

#####答案1


select studentname,gradename,subjectname,examdate,studentresult
from result r
join student s
on r.studentno=s.studentno
join course c
on r.subjectno=c.subjectno
join grade g
on c.gradeid=g.gradeid
where examdate=
(
select max(examdate) from result
where studentno=r.studentno and subjectno=r.subjectno
)
order by convert(studentname using gbk),gradename,subjectname
;


#我的----有问题--已修正,内连接先连谁不讲究,但是什么表相邻是讲究的


select studentname,gradename,subjectname,examdate,studentresult
from grade
join course 
on grade.gradeid=course.gradeid
join result r
on course.subjectno=r.subjectno
join student
on student.studentno=r.studentno
where examdate=
(
select max(examdate) from result
where studentno=r.studentno and subjectno=r.subjectno
)
order by convert(studentname using gbk),gradename,subjectname
;

#我的----有问题---会串年级,即不是这个年级学的课却展示了


select studentname,gradename,subjectname,examdate,studentresult
from grade
join student 
on student.gradeid=grade.gradeid
join result r
on student.studentno=r.studentno
join course
on course.subjectno=r.subjectno
where examdate=
(
select max(examdate) from result
where studentno=r.studentno and subjectno=r.subjectno
)
order by convert(studentname using gbk),gradename,subjectname
;

 

 

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