题解 | #作答试卷得分大于过80的人的用户等级分布#

# SQL, 作答分数>80，按用户等级分组，计算不同等级人数
SELECT level, COUNT(uid) AS level_cnt
FROM user_info
WHERE uid IN(
            SELECT r.uid
            FROM examination_info AS i 
            LEFT JOIN exam_record AS r ON i.exam_id=r.exam_id
            WHERE i.tag = 'SQL' AND r.score > 80
            ) 
GROUP BY level
ORDER BY level_cnt DESC;