Question

Formatted question description: https://leetcode.ca/all/185.html

185. Department Top Three Salaries

Level

Hard

Description

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

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 85000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
| 7  | Will  | 70000  | 1            |
+----+-------+--------+--------------+

The Department table 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 (order of rows does not matter).

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

Explanation:

In IT department, Max earns the highest salary, both Randy and Joe earn the second highest salary, and Will earns the third highest salary. There are only two employees in the Sales department, Henry earns the highest salary while Sam earns the second highest salary.

Solution

Join the tables Employee and Department and select the three columns of each entry. To obtain the top three salaries in each of the department, in Employee table, only select the entries that has less than 3 entries that has the same DepartmentId and a higher Salary.

SELECT
    d.Name AS 'Department', e1.Name AS 'Employee', e1.Salary
FROM
    Employee e1
JOIN
    Department d
ON e1.DepartmentId = d.Id
WHERE
    3 > (
        SELECT
            COUNT(DISTINCT e2.Salary)
        FROM
            Employee e2
        WHERE
            e2.Salary > e1.Salary
        AND e1.DepartmentId = e2.DepartmentId
        )
;


-- use group by

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) <= 3
ORDER BY D.Name, E.Salary DESC

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