[英]How to write SQL to select rows that has the max(value) of each group?
表格如下:
employee, department, salary
Jack, 1, 400
Greg, 2, 350
John, 1, 450
Kate, 2, 420
Jane, 3, 300
Jessy, 2, 400
Kevin, 3, 380
我希望这样做:选择包含每个部门最高薪水的行,我希望返回:
John, 1, 450
Jessy, 2, 400
Kevin, 3, 380
在这里,部门1,约翰的薪水最高,所以我选择这整行。
怎么写这个SQL?
一种方法使用相关子查询:
select e.*
from employee e
where e.salary = (select max(e2.salary) from employee e2 where e2.department = e.department);
从员工e1的e1.salary中选择e1。*(从员工e2的e2.department = e1.department中选择max(e2.salary));
我通常使用窗口函数解决此问题:
select employee, department, salary
from (
select employee, department, salary,
dense_rank() over (partition by department order by salary desc) as rnk
from employee_table
) t
where rnk = 1;
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