[LeetCode] 184. Department Highest Salary

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Problem

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

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+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Jim   | 90000  | 1            |
| 3  | Henry | 80000  | 2            |
| 4  | Sam   | 60000  | 2            |
| 5  | Max   | 90000  | 1            |
+----+-------+--------+--------------+

The Department table holds all departments of the company.

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+----+----------+
| 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, your SQL query should return the following rows (order of rows does not matter).

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

Explanation:

Max and Jim both have the highest salary in the IT department and Henry has the highest salary in the Sales department.

Explanation

  1. We can LEFT JOIN two tables.

  2. In a subquery, use MAX and GROUP BY Employee.DepartmentId to get the maximum salary and DepartmentId, then first table’s salary and second table’s Department.id IN that subquery’s max salary and DepartmentId.

  3. Select all the required columns from that first table.

Solution

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# Write your MySQL query statement below
SELECT d1.Name as Department, e1.Name as Employee, e1.Salary as Salary
FROM Employee as e1
LEFT JOIN Department as d1
ON e1.DepartmentId = d1.Id
WHERE (e1.Salary, d1.Id) IN (
    SELECT MAX(Salary), DepartmentId
    FROM Employee
    GROUP BY DepartmentId
);