按列查询上次数据

Question

我有这个数据；

date        owner   p.code  product
----        -----   -----   ------
21.08.2020  Micheal   5    apple
22.08.2020  Micheal   5    apple
15.08.2020  George    4    biscuit
14.08.2020  George    4    biscuit
10.08.2020  Micheal   4    biscuit
23.08.2020  Alice     2    pear
15.08.2020  Alice     2    pear
14.08.2020  Micheal   2    pear
11.08.2020  Micheal   2    pear

我想将它们分组到产品并显示最后日期和最后所有者。

像这样；

date         owner  p.code  product
----         -----   ------  ------
22.08.2020  Micheal    5    apple
15.08.2020  George     4    biscuit
23.08.2020  Alice      2    pear

Answer 1

您可以使用 window 函数：

select *
from (
    select t.*, row_number() over(partition by product order by date desc) rn 
    from mytable t
) t
where rn = 1

Answer 2

在 Oracle 中，您可以使用 group by:

select product, code,
       max(date) as max_date,
       max(owner) keep (dense_rank first order by date desc) as owner_at_max_date
from t
group by product, code;

keep 语法是 Oracle 实现 first() 聚合函数的相当冗长的方式。