Question

Formatted question description: https://leetcode.ca/all/184.html

The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id.

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
+----+-------+--------+--------------+
The Department table holds all departments of the company.

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+
Write a SQL query to find employees who have the highest salary in each of the departments. For the above tables, Max has the highest salary in the IT department and Henry has the highest salary in the Sales department.

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| Sales      | Henry    | 80000  |
+------------+----------+--------+

Algorithm

Join the two tables together, and then mark all the columns required in the result table, and then find the highest salary, using the Max keyword.

A pair (a,b) in ( block returning tuple)

Code

SQL

SELECT
    Department.name AS 'Department',
    Employee.name AS 'Employee',
    Employee.Salary
FROM
    Employee
JOIN -- default is inner join
    Department
ON Employee.DepartmentId = Department.Id
WHERE
    (Employee.DepartmentId , Employee.Salary) IN -- so that if tie, both will appear in result
    (
        SELECT
            DepartmentId, MAX(Salary)
        FROM
            Employee
        GROUP BY DepartmentId
    )
;

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