题解 | #每类视频近一个月的转发量/率#

SELECT
    tag,
    SUM(IF(if_retweet=1, 1, 0)) AS retweet_cut,
    ROUND(AVG(IF(if_retweet=1, 1, 0)), 3) AS retweet_rate
FROM tb_user_video_log t1
JOIN tb_video_info t2 USING(video_id)
WHERE DATEDIFF((SELECT MAX(end_time) FROM tb_user_video_log), end_time) < 30
GROUP BY tag
ORDER BY retweet_rate DESC

老是忘记不能直接在函数里直接写MAX()，要用一个子查询，麻了，，，