SQL面试题-近30日内用户最新观看电影题材

用户登录视频网站，有时当日未观看电影，但需要分析用户喜欢的电影题材，就需要补充近30日内最新观看电影的题材。

用户ID	登录日期	观看电影
1	2023-01-05	爱情
1	2023-01-17
1	2023-01-29	恐怖
1	2023-02-15	科幻
1	2023-03-05
2	2023-01-07	传记
2	2023-02-25	记录
2	2023-02-26

要点：使用开窗函数按时间戳排序，通过range between来限制时间范围。日期与电影题材拼接，若电影题材为空，拼接结果为null，取最大值，就是用户最近观看的电影题材。

select
    id,
    dt,
    dt_timestamp,
    type,
    substr(last_30d_type,11)  last_30d_type
from
(
    select
        id,
        dt,
        unix_timestamp(dt,'yyyy-MM-dd') dt_timestamp,
        type,
        max(concat(dt,type)) over (partition by id order by unix_timestamp(dt,'yyyy-MM-dd') range between  2505600 preceding and current row) as last_30d_type
    from
    (
        select 1 as id, '2023-01-05' as dt, '爱情' as type
        union all select 1 as id, '2023-01-17' as dt, null   as type
        union all select 1 as id, '2023-01-29' as dt, '恐怖' as type
        union all select 1 as id, '2023-02-15' as dt, '科幻' as type
        union all select 1 as id, '2023-03-05' as dt, null   as type
        union all select 2 as id, '2023-01-07' as dt, '传记' as type
        union all select 2 as id, '2023-02-25' as dt, '记录' as type
        union all select 2 as id, '2023-02-26' as dt, null   as type
    ) a 
) b