我有一个表,里面的数据是这样的
映射关系
1个task_id被映射到多个task_detail_id(1对多)
Task_detail_id Task_id Creation_date
1 20 2020-05-02 20:28:23.354
2 21 2020-05-02 20:28:23.354
3 22 2020-05-02 19:28:23.354
4 22 2020-05-02 18:28:23.354
5 22 2020-05-02 17:28:23.354
6 22 2020-05-02 16:28:23.354
7 22 2020-05-02 15:28:23.354
8 23 2020-05-02 10:28:23.354
9 24 2020-05-02 09:28:23.354
10 24 2020-05-02 08:28:23.354
11 24 2020-05-02 07:28:23.354
我想要的是遍历表,并获取记录,就像 相同的task_id存在2次以上,则取前2名(最新)。 的记录
采样输出
Task_detail_id Task_id Creation_date
1 20 2020-05-02 20:28:23.354
2 21 2020-05-02 20:28:23.354
3 22 2020-05-02 19:28:23.354
4 22 2020-05-02 18:28:23.354
8 23 2020-05-02 10:28:23.354
9 24 2020-05-02 09:28:23.354
10 24 2020-05-02 08:28:23.354
这通常是用窗口函数来完成的。
select task_detail_id, task_id, creation_date
from (
select task_detail_id, task_id, creation_date,
row_number() over (partition by task_id order by creation_date desc) as rn
from data
) t
where rn <= 2
order by task_detail_id, task_id;