题解 | #浙大不同难度题目的正确率#

SELECT
  qd.difficult_level,
  SUM(CASE WHEN qpd.result = 'right' THEN 1 ELSE 0 END) / COUNT(qpd.id) as correct_rate
FROM
  user_profile up
inner JOIN
  question_practice_detail qpd ON up.device_id = qpd.device_id
inner JOIN
  question_detail qd ON qpd.question_id = qd.question_id
WHERE
  up.university = '浙江大学'
GROUP BY
  qd.difficult_level
ORDER BY
  correct_rate ;