SQL159 每个创作者每月的涨粉率及截止当前的总粉丝量
描述
用户-视频互动表tb_user_video_log
| id | uid | video_id | start_time | end_time | if_follow | if_like | if_retweet | comment_id |
| 1 | 101 | 2001 | 2021-09-01 10:00:00 | 2021-09-01 10:00:20 | 0 | 1 | 1 | NULL |
| 2 | 105 | 2002 | 2021-09-10 11:00:00 | 2021-09-10 11:00:30 | 1 | 0 | 1 | NULL |
| 3 | 101 | 2001 | 2021-10-01 10:00:00 | 2021-10-01 10:00:20 | 1 | 1 | 1 | NULL |
| 4 | 102 | 2001 | 2021-10-01 10:00:00 | 2021-10-01 10:00:15 | 0 | 0 | 1 | NULL |
| 5 | 103 | 2001 | 2021-10-01 11:00:50 | 2021-10-01 11:01:15 | 1 | 1 | 0 | 1732526 |
| 6 | 106 | 2002 | 2021-10-01 10:59:05 | 2021-10-01 11:00:05 | 2 | 0 | 0 | NULL |
（uid-用户ID, video_id-视频ID, start_time-开始观看时间, end_time-结束观看时间, if_follow-是否关注, if_like-是否点赞, if_retweet-是否转发, comment_id-评论ID）
短视频信息表tb_video_info
| id | video_id | author | tag | duration | release_time |
| 1 | 2001 | 901 | 影视 | 30 | 2021-01-01 07:00:00 |
| 2 | 2002 | 901 | 美食 | 60 | 2021-01-01 07:00:00 |
| 3 | 2003 | 902 | 旅游 | 90 | 2020-01-01 07:00:00 |
| 4 | 2004 | 902 | 美女 | 90 | 2020-01-01 08:00:00 |
（video_id-视频ID, author-创作者ID, tag-类别标签, duration-视频时长, release_time-发布时间）
问题：计算2021年里每个创作者每月的涨粉率及截止当月的总粉丝量
注：
- 涨粉率=(加粉量 - 掉粉量) / 播放量。结果按创作者ID、总粉丝量升序排序。
- if_follow-是否关注为1表示用户观看视频中关注了视频创作者，为0表示此次互动前后关注状态未发生变化，为2表示本次观看过程中取消了关注。
输出示例：
示例数据的输出结果如下
| author | month | fans_growth_rate | total_fans |
| 901 | 2021-09 | 0.500 | 1 |
| 901 | 2021-10 | 0.250 | 2 |
解释：
示例数据中表tb_user_video_log里只有视频2001和2002的播放记录，都来自创作者901，播放时间在2021年9月和10月；其中9月里加粉量为1，掉粉量为0，播放量为2，因此涨粉率为0.500（保留3位小数）；其中10月里加粉量为2，掉份量为1，播放量为4，因此涨粉率为0.250，截止当前总粉丝数为2。
示例1
输入：
DROP TABLE IF EXISTS tb_user_video_log, tb_video_info;
CREATE TABLE tb_user_video_log (
id INT PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
uid INT NOT NULL COMMENT '用户ID',
video_id INT NOT NULL COMMENT '视频ID',
start_time datetime COMMENT '开始观看时间',
end_time datetime COMMENT '结束观看时间',
if_follow TINYINT COMMENT '是否关注',
if_like TINYINT COMMENT '是否点赞',
if_retweet TINYINT COMMENT '是否转发',
comment_id INT COMMENT '评论ID'
) CHARACTER SET utf8 COLLATE utf8_bin;
CREATE TABLE tb_video_info (
id INT PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID',
video_id INT UNIQUE NOT NULL COMMENT '视频ID',
author INT NOT NULL COMMENT '创作者ID',
tag VARCHAR(16) NOT NULL COMMENT '类别标签',
duration INT NOT NULL COMMENT '视频时长(秒数)',
release_time datetime NOT NULL COMMENT '发布时间'
)CHARACTER SET utf8 COLLATE utf8_bin;
INSERT INTO tb_user_video_log(uid, video_id, start_time, end_time, if_follow, if_like, if_retweet, comment_id) VALUES
(101, 2001, '2021-09-01 10:00:00', '2021-09-01 10:00:20', 0, 1, 1, null)
,(105, 2002, '2021-09-10 11:00:00', '2021-09-10 11:00:30', 1, 0, 1, null)
,(101, 2001, '2021-10-01 10:00:00', '2021-10-01 10:00:20', 1, 1, 1, null)
,(102, 2001, '2021-10-01 10:00:00', '2021-10-01 10:00:15', 0, 0, 1, null)
,(103, 2001, '2021-10-01 11:00:50', '2021-10-01 11:01:15', 1, 1, 0, 1732526)
,(106, 2002, '2021-10-01 10:59:05', '2021-10-01 11:00:05', 2, 0, 0, null);
INSERT INTO tb_video_info(video_id, author, tag, duration, release_time) VALUES
(2001, 901, '影视', 30, '2021-01-01 7:00:00')
,(2002, 901, '影视', 60, '2021-01-01 7:00:00')
,(2003, 902, '旅游', 90, '2020-01-01 7:00:00')
,(2004, 902, '美女', 90, '2020-01-01 8:00:00');输出：
901|2021-09|0.500|1
901|2021-10|0.250|2第一步：算出关注和掉粉
select
sum(
case
when if_follow = "1" then 1
when if_follow = "2" then -1
else 0
end
)
from
tb_user_video_log
第二步：连表进行根据作者和时间分组
select
sum(
case
when if_follow = "1" then 1
when if_follow = "2" then -1
else 0
end
)
from
tb_user_video_log tb1
left join tb_video_info tb2 on tb1.video_id = tb2.video_id
group by
author,
month
第三步：算出关注率
select
author,
date_format(start_time, '%Y-%m') month,
round(
sum(
case
when if_follow = "1" then 1
when if_follow = "2" then -1
else 0
end
) / count(1),
3
)
from
tb_user_video_log tb1
left join tb_video_info tb2 on tb1.video_id = tb2.video_id
group by
author,
month
order by
author,
total_fans
**这里需要知道窗口函数 over(partition by 分组列名 order by 排序列名 rows between 开始位置 and 结束位置)
第四步，使用窗口函数算出粉丝量
select
author,
date_format(start_time, '%Y-%m') month,
round(
sum(
case
when if_follow = "1" then 1
when if_follow = "2" then -1
else 0
end
) / count(1),
3
),
sum(
sum(
case
when if_follow = "1" then 1
when if_follow = "2" then -1
else 0
end
)
) over(
partition by author
order by
date_format(tb1.start_time, '%Y-%m')
) total_fans
from
tb_user_video_log tb1
left join tb_video_info tb2 on tb1.video_id = tb2.video_id
where
year(tb1.start_time) = "2021"
group by
author,
month
order by
author,
total_fans
