题解 | #统计有未完成状态的试卷的未完成数和未完成率#
统计有未完成状态的试卷的未完成数和未完成率
http://www.nowcoder.com/practice/69fc2b1df4144c0991e4b8280d8aba27
select * from (
select exam_id,
sum(if(submit_time is null,1,0)) as incomplete_cnt
,round(sum(if(submit_time is null,1,0))/count(*),3) as incomplete_rate
from exam_record group by exam_id ) t1 where t1.incomplete_cnt != 0


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