题解 | #月总刷题数和日均刷题数#

SELECT
  DATE_FORMAT(submit_time, '%Y%m') submit_month,
  COUNT(*) month_q_cnt,
  ROUND(COUNT(*) / AVG(DAY(LAST_DAY(submit_time))), 3) avg_day_q_cnt
FROM
  practice_record
WHERE
  YEAR(submit_time) = '2021'
  AND submit_time IS NOT NULL
GROUP BY
  DATE_FORMAT(submit_time, '%Y%m')
  
UNION ALL

SELECT
  '2021汇总' submit_month,
  COUNT(*) month_q_cnt,
  ROUND(COUNT(*) / 31, 3) avg_day_q_cnt
FROM
  practice_record
WHERE
  YEAR(submit_time) = '2021'
  AND submit_time IS NOT NULL
ORDER BY
  submit_month;

GROUP BY

DATE_FORMAT(submit_time, '%Y%m') 就是group by month