SQL练习
Less than 1 minute
1280
cross join 和嵌套 join 一定要掌握
1280. 学生们参加各科测试的次数 - 力扣（LeetCode）
select s.student_id,student_name,sub.subject_name,IFNULL(count_exams.attended_exams,0) as attended_exams
from Students as s
cross join Subjects as sub
left join (
select student_id,subject_name,count(*) as attended_exams
from Examinations
group by student_id,subject_name
) count_exams
on s.student_id = count_exams.student_id and sub.subject_name = count_exams.subject_name
group by s.student_id, sub.subject_name
order by s.student_id,sub.subject_name