Select 每个员工的 max(date) 辆车

Question

我需要以下问题的代码：

我有一个 table 这样的：

Employee	Year	Month	Car
Tom	2021	9	Ford
Tom	2021	10	Ford
Tom	2021	11	Ford
Tom	2021	12	Renault
Tom	2022	1	Renault
Mark	2021	12	VW
Mark	2022	1	VW
Mark	2022	2	VW
Joe	2021	8	Opel
Joe	2021	9	Tesla
Joe	2021	10	Ferrari

而且我需要员工在最后可能的日期使用的汽车。所以结果应该是：

Employee	Car
Tom	Renault
Mark	VW
Joe	Ferrari

有：

select employee, max(year || month) from table.cars
group by employee

我得到每个员工的最大（日期），但我不知道如何加入汽车到最大（日期）。

怎样才能得到我想要的结果？

Answer 1

可以使用ROW_NUMBER()解析函数如

SELECT Employee, Car
  FROM (SELECT ROW_NUMBER() OVER 
                           (PARTITION BY Employee ORDER BY year DESC, month DESC) AS rn,
               c.*
          FROM cars c)
 WHERE rn = 1

前提是年月的数据类型是字符串类型，那么可以把ORDER BY year DESC, month DESC部分替换成

ORDER BY TO_NUMBER(TRIM(year)) DESC, TO_NUMBER(TRIM(month)) DESC

Answer 2

with t as
(
  select *,
        row_number() over (partition by employee order by year desc, month desc) rn
  from cars 
) 
select employee, car 
from t
where rn = 1

Answer 3

试试这个：

select employee, car 
from ( 
        Select *, ROW_NUMBER(partition by employee order by year, month DESC) as row_number
        from cars
        )a
Where row_number = 1

Select 每个员工的 max(date) 辆车

Select car of max(date) for every employee

sql

oracle

greatest-n-per-group