How to write SQL to select rows that has the max(value) of each group?

Question

The table is like below:

employee, department, salary

Jack, 1, 400
Greg, 2, 350
John, 1, 450
Kate, 2, 420
Jane, 3, 300
Jessy, 2, 400
Kevin, 3, 380

I wish to do: Select the row that contains the highest salary of each department, I expect to return:

John,  1, 450
Jessy, 2, 400
Kevin, 3, 380

Here for department 1, John has the highest salary, so I select this whole row.

How to write this SQL?

Answer 1

One method uses a correlated subquery:

select e.*
from employee e
where e.salary = (select max(e2.salary) from employee e2 where e2.department = e.department);

Answer 2

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））；

Answer 3

I typically solve that using window functions:

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;