题解 | #查询每天刷题通过数最多的前二名用户id和刷题数#

/*查询思路
1.考虑到每个用户每天不止刷一类题目，因此首先查询每个用户每天刷各类题目的总数 p_count，按user_id和date分组，得到临时表t1
2.对临时表t1按照题目要求，以date分组并按照p_count排序，得到临时表t2
3.对临时表t2按照题目要求，过滤rn前两名的用户答题信息
*/

SELECT t2.date,t2.user_id,t2.p_count AS pass_count
FROM (
    SELECT t1.date,t1.user_id,t1.p_count,DENSE_RANK() OVER (PARTITION BY t1.date ORDER BY p_count DESC) rn 
    FROM (
        SELECT date,user_id,SUM(pass_count) p_count 
        FROM questions_pass_record
        GROUP BY user_id,date) AS t1  
    ) AS t2
WHERE t2.rn BETWEEN 1 AND 2
ORDER BY t2.date