Oracle SQL 11g获得每个类别的最新信息

Question

使用下表。我需要获取每个date_joined中最新的DEPT。

 __________________________________
| DEPT     | DATE_JOINED | MANAGER |
|----------------------------------|
|  Produce | 30-JUL-15   | George  |
|  Grocery | 05-FEB-18   | Michael |
|  Produce | 30-JAN-18   | Joe     |
|  Grocery | 01-OCT-10   | Susan   |
|  Grocery | 25-SEP-17   | Sam     |    
|  Produce | 03-JUN-18   | Lizzy   |
|__________________________________|

想要的结果是每个部门加入的最新日期：

 __________________________________
| DEPT     | DATE_JOINED | MANAGER |
|----------------------------------|
|  Grocery | 05-FEB-18   | Michael |
|  Produce | 03-JUN-18   | Lizzy   |
|__________________________________|

Answer 1

一种简单的方法使用相关子查询：

select t.*
from t
where t.date_joined = (select max(t2.date_joined) from t t2 where t2.dept = t.dept);

但是，在这种情况下，我的运气（在性能方面）不错：

select dept, max(date_joined) as date_joined,
       max(manager) keep (dense_rank first order by date_joined desc) as manager
from t
group by dept;