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 exam_id
, SUM(CASE WHEN submit_time IS NULL THEN 1 ELSE 0 END) AS incomplete_cnt
, ROUND(SUM(CASE WHEN submit_time IS NULL THEN 1 ELSE 0 END) / COUNT(start_time),3) AS complete_rate
FROM exam_record
GROUP BY exam_id
HAVING COUNT(start_time) != COUNT(submit_time)
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