题解 | #统计作答次数#
统计作答次数
https://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
select sum(if(start_time is not null,1,0)) total_pv, sum(if(submit_time is not null,1,0))complete_pv, count(distinct (if(score is not null,1,0 ))) complete_exam_cnt from exam_record