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