department-highest-salary.sql

# Time:  O(n^2)
# Space: O(n)
# 
# 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  |
# +------------+----------+--------+
# 
# Write your MySQL query statement below
SELECT d.Department AS Department, e.Name AS Employee, d.Salary AS Salary
FROM (SELECT Department.Id AS DepartmentId, Department.Name AS Department, emp.Salary AS Salary
        FROM Department JOIN (SELECT DepartmentId, MAX(Salary) AS Salary FROM Employee GROUP BY DepartmentId) emp
        ON Department.Id = emp.DepartmentId) d 
      JOIN Employee e 
      ON e.DepartmentId = d.DepartmentId and e.Salary = d.Salary

# Write your MySQL query statement below
SELECT Department.Name AS Department, Employee.Name AS Employee, Employee.Salary AS Salary
FROM Department JOIN Employee ON Employee.DepartmentId = Department.Id
WHERE Employee.Salary IN (SELECT MAX(e.Salary) FROM Employee e WHERE e.DepartmentId = Employee.DepartmentId)

SELECT D.Name as Department, E.Name as Employee, E.Salary 
  FROM Department D, Employee E, Employee E2  
  WHERE D.ID = E.DepartmentId and E.DepartmentId = E2.DepartmentId and 
  E.Salary <= E2.Salary
  group by D.ID,E.Name having count(distinct E2.Salary) = 1
  order by D.Name desc