leetcode 1280 學生們參加各科測試的次數

leetcode 1280 學生們參加各科測試的次數

select s.student_id, s.student_name, st.subject_name, if(e.result, e.result, 0) as attended_exams from Students s 
join Subjects st
left join (
    select student_id, subject_name, count(*) as result from Examinations 
    group by student_id, subject_name  
) e
on s.student_id = e.student_id and st.subject_name = e.subject_name
order by s.student_id, st.subject_name

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