题解 | 统计有未完成状态的试卷的未完成数和未完成率
select
exam_id,
sum(if (submit_time is null, 1, 0)) incomplete_cnt,
round(
sum(if (submit_time is null, 1, 0)) / count(exam_id),
3
) incomplete_rate
from
test.exam_record
group by
exam_id
having
incomplete_cnt != 0
