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, incomplete_cnt,
ROUND(incomplete_cnt / record_cnt, 3) AS incomplete_rate
FROM (
SELECT exam_id,
COUNT(start_time) AS record_cnt,
COUNT(IF(submit_time IS NULL, exam_id, NULL)) AS incomplete_cnt
FROM exam_record
GROUP BY exam_id
)record_table
WHERE incomplete_cnt > 0
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