题解 | #每类视频近一个月的转发量/率#

该题最难的部分就是控制在近30天内，而且得注意该题得近30天，实际是算29天。

SELECT
    tag,
    SUM(if_retweet = 1) AS retweet_cut,
    ROUND(SUM(if_retweet = 1) / COUNT(tag), 3) AS retweet_rate
FROM
    tb_user_video_log
    left join tb_video_info using (video_id)
WHERE
    DATEDIFF (
        DATE (
            (
                SELECT
                    MAX(start_time)
                FROM
                    tb_user_video_log
            )
        ),
        DATE (start_time)
    ) < 30
GROUP BY
    tag
ORDER BY
    retweet_rate DESC;