Write a query for the highest salary per department.

Short answer: GROUP BY DepartmentId with MAX(Salary), or use RANK/DENSE_RANK PARTITION BY DepartmentId to also return employee names tied for max.

Sample solution

-- Aggregate only
SELECT DepartmentId, MAX(Salary) AS MaxSalary
FROM Employees
GROUP BY DepartmentId;

-- Employees earning the max in their department
SELECT EmpId, Name, DepartmentId, Salary
FROM (
    SELECT *, DENSE_RANK() OVER (
        PARTITION BY DepartmentId ORDER BY Salary DESC
    ) AS rnk
    FROM Employees
) t
WHERE rnk = 1;

If they want names, window functions beat a join-back to MAX aggregates.