题解 | #统计作答次数#
统计作答次数
https://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
select count(uid) as total_pv ,count(score) as complete_pv ,count(distinct if(score is null,null,exam_id)) as complete_exam_cnt from exam_record
主要是在select中去过滤其他字段
如果score为null,那么该行的exam_id就为null,不会被统计到count里
select count(distinct if(score is null,null,exam_id)) as complete_exam_cnt