185_Department Top Three Salaries

TheEmployeetable holds all employees. Every employee has an Id, 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            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
+----+-------+--------+--------------+

TheDepartmenttable holds all departments of the company.

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

Write a SQL query to find employees who earn the top three salaries in each of the department. For the above tables, your SQL query should return the following rows.

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Randy    | 85000  |
| IT         | Joe      | 70000  |
| Sales      | Henry    | 80000  |
| Sales      | Sam      | 60000  |
+------------+----------+--------+

Solution 1:using correlated subqueries and joins

SELECT D.Name AS Department, E1.Name AS Employee, E1.Salary AS Salary
FROM Department AS D
    JOIN Employee AS E1 ON D.Id = E1.DepartmentId
WHERE 3 >
    (
    SELECT COUNT(DISTINCT E2.Salary)
    FROM Employee AS E2
    WHERE E2.Salary > E1.Salary 
        AND E2.DepartmentId = E1.DepartmentId
    )
ORDER BY Department, Salary
;

Solution 2: only using joins

SELECT d.Name as Department, e.Name as employee, e.Salary
FROM Employee e
    JOIN Department d ON e.DepartmentId = d.Id
WHERE (e.DepartmentId, e.Salary) IN
    (SELECT e1.DepartmentId, e1.Salary
    FROM Employee e1
        LEFT JOIN Employee e2 ON e1.DepartmentId = e2.DepartmentId AND e1.Salary < e2.Salary
    GROUP BY e1.DepartmentId, e1.Salary
    HAVING count(distinct e2.Salary) < 3);

Solution 3: use group by

SELECT department.Name Department, e1.Name Employee, e1.Salary
FROM employee e1
    JOIN department ON e1.DepartmentId = department.Id
    LEFT JOIN employee e2 ON e1.DepartmentId = e2.DepartmentId AND e1.Salary < e2.Salary
GROUP BY e1.Id
HAVING count(distinct e2.Salary) < 3
ORDER BY department.Name, e1.Salary desc;