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