-- 统计作答SQL类别的试卷得分大于过80的人的用户等级分布,按数量降序排序,
-- 1、关联查询 2、过滤 3、分组统计,等级
SELECT
c.level, COUNT(1) level_cnt
FROM
exam_record a
INNER JOIN
examination_info b ON a.exam_id = b.exam_id
INNER JOIN
user_info c ON a.uid = c.uid
WHERE
b.tag = 'SQL' AND a.score > 80
GROUP BY c.level
ORDER BY level_cnt DESC;