题解 | #统计作答次数#

select count(*)                         as total_pv,
       sum(if(score is not null, 1, 0)) as coplete_pv,
       (select count(*)
        from (select exam_id
              from exam_record
              where score is not null
              group by exam_id) as new) as complete_exam_cnt
from exam_record;