MySQL: ROW_NUMBER () counts duplicates as separate rows - mysql

Question

I have two tables. Table of employees Employee and departments Department.
The Employee table looks like this:
+----+-------+--------+--------------+
| 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 looks like this:
+----+----------+
| Id | Name |
+----+----------+
| 1 | IT |
| 2 | Sales |
+----+----------+
I want to write a query that for each department will output employees and a number indicating the salary rating. (If the salary is the maximum in the department, the number is 1. If there are two identical salaries in the department, then their rating number must be the same).
I implemented this query using the window function ROW_NUMBER():
SELECT
d.Name Department,
e.Name Employee,
e.Salary,
ROW_NUMBER() OVER (
PARTITION BY d.Name
ORDER BY e.Salary DESC
) SalaryRating,
FROM
Employee e
LEFT JOIN Department d
ON e.DepartmentId = d.Id;
This query outputs the following data:
Department Employee Salary SalaryRating
IT Max 90000 1
IT Joe 85000 2
IT Randy 85000 3
IT Will 70000 4
IT Janet 69000 5
Sales Henry 80000 1
Sales Sam 60000 2
There is a mistake. Randy SalaryRating value is 3, but it should be 2, because he has the same salary as Joe.
What is the error in my query? How to fix it?

Answer 1

You can use DENSE_RANK
SELECT
d.Name Department,
e.Name Employee,
e.Salary,
DENSE_RANK() OVER (
PARTITION BY d.Name
ORDER BY e.Salary DESC
) SalaryRating,
FROM
Employee e
LEFT JOIN Department d
ON e.DepartmentId = d.Id;