题解 | #统计作答次数#
统计作答次数
http://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
select count(er.id) as total_pv, sum(case when er.submit_time is not null then 1 else 0 end) as complete_pv, count(distinct case when er.submit_time is not null then er.exam_id end) as complete_exam_cnt from exam_record er ;