SQL implementation of LeetCode (184. The highest salary in the department)

[LeetCode] 184. Department Highest Salary

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 |
+------------+----------+--------+

This question gives us two tables, Employee and Department, and asks us to find the person with the highest salary in the department. In fact, this question is a combination of Second Highest Salary and Combine Two Tables . We need to combine the two tables and find the highest salary. So we first intersect the two tables, then mark the required columns in the result table, and then find the highest salary. We use the Max keyword to achieve this. See the code below:

Solution 1:

SELECT d.Name AS Department, e1.Name AS Employee, e1.Salary FROM Employee e1
JOIN Department d ON e1.DepartmentId = d.Id WHERE Salary IN 
(SELECT MAX(Salary) FROM Employee e2 WHERE e1.DepartmentId = e2.DepartmentId);

We can also use Where to join the two tables without using the Join keyword, and then find the highest salary in the same way as above:

Solution 2:

SELECT d.Name AS Department, e.Name AS Employee, e.Salary FROM Employee e, Department d
WHERE e.DepartmentId = d.Id AND e.Salary = (SELECT MAX(Salary) FROM Employee e2 WHERE e2.DepartmentId = d.Id);

The following method does not use the Max keyword, but uses the >= symbol, which achieves the same effect as the Max keyword. See the code below:

Solution 3:

SELECT d.Name AS Department, e.Name AS Employee, e.Salary FROM Employee e, Department d
WHERE e.DepartmentId = d.Id AND e.Salary >= ALL (SELECT Salary FROM Employee e2 WHERE e2.DepartmentId = d.Id);

Similar topics:

Second Highest Salary

Combine Two Tables

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