题解 | #统计作答次数#

#方法一
select
    count(exam_id) total_pv,
    count(score) complete_pv,
    count(
        distinct exam_id,
        score is not null
        or null
    ) complete_exam_cnt
from
    exam_record

#方法二
select
    count(*) total_pv,
    count(submit_time) complete_pv,
    (
        select 
            count(distinct exam_id) 
        from exam_record 
        where submit_time is not null
    ) complete_exam_cnt
from
    exam_record