如何構建查詢？任何想法？

Question

3表：

馬克表：

student_id sa_id marks 
1   1 75 
1   2 80 
1   3 100 
2   4 85 
2   5 90 
2   6 60 

當然表：

course_code sat_id name_code 
AAA 100   1  midterm1 
AAA 100   2  midterm2 
AAA 100   3  final 
BBB 200   4  midterm1 
BBB 200   5  midterm2 
BBB 200   6  final 

變換表：

sa_id  sat_id 
1   1 
2   2 
3   3 
4   4 
5   5 
6   6  

select course.course_code, mark.marks 
from mark 
    left outer join transform on transform.sa_id = mark.sa_id 
    left outer join course on course.sat_id = transfrom.sat_id 
where course.name_code = 'midterm1' 

在上面的查詢只midterm1結果，我們也可以提取MID2和最終

select mark.student_id,course.course_code, mark.marks, course.name_code 
from mark 
    left outer join transform on transform.sa_id = mark.sa_id 
    left outer join course on course.sat_id = transfrom.sat_id 
order by mark.student_id, course.course_code 

結果會給：

student_id course_code marks name_code 
1   AAA 100  75  midterm1 
1   AAA 100  80  midterm2 
1   AAA 100  100 final 
2   BBB 200  85  midterm1 
2   BBB 200  90  midterm2 
2   BBB 200  60  final 

因此，如何建立查詢，應該是

student_id course_code midterm1 midterm2 final 
1    AAA 100  75   80  100 
2    BBB 200  85   90  60 

Answer 1

您可以使用情況時，按組（和一個假的聚合功能）

select 
     student_id 
    , course_code 
    , max(case when name_code ='midterm1' then mark else null) midterm1 
    , max(case when name_code ='midterm2' then mark else null) midterm2  
    , max(case when name_code ='final' then mark else null) final 
from mark 
left outer join transform on transform.sa_id = mark.sa_id 
left outer join course on course.sat_id = transfrom.sat_id 
group by student_id, course_code 
order by mark.student_id, course.course_code 

但是，如果你不喜歡聚集函數的，你可以使用一個3 seleft加入上標記

select 
     mm1.student_id 
     , mm1.course_code 
     , mm1.mark midterm1 
     , mm2.mark midterm2 
     , mm3.mark finale  
    from mark as mm1 
    left join mark as mm2 on mm1.student_id = mm2.student_id and mm1.course_code = mm2.course_code 
    left join mark as mm3 on mm1.student_id = mm3.student_id and mm1.course_code = mm3.course_code 
    left outer join transform on transform.sa_id = mm1.sa_id 
    left outer join course on course.sat_id = transfrom.sat_id 
    where mm1.name_code = 'midterm1' 
    and mm2.name_code = 'midterm2' 
    and mm3.name_code = 'final'