题解 | #每份试卷每月作答数和截止当月的作答总数。#
每份试卷每月作答数和截止当月的作答总数。
http://www.nowcoder.com/practice/5f1cbe74c682485aa73e4c2b30f04a62
WITH a1 AS (
SELECT exam_id, DATE_FORMAT(start_time,'%Y%m') AS start_month, COUNT(start_time) AS month_cnt
FROM exam_record
GROUP BY exam_id, start_month
ORDER BY exam_id, start_month
)
SELECT *, SUM(month_cnt) OVER (PARTITION BY exam_id ORDER BY start_month)
FROM a1
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