Department Highest Salary

Department Highest Salary

1. What is this problem about?

The Department Highest Salary interview question is a fundamental SQL challenge. You are given two tables: Employee (with names, salaries, and department IDs) and Department (with names and IDs). Your task is to find the employees who have the highest salary in each of their respective departments. This Department Highest Salary coding problem requires identifying a maximum value within a group and then retrieving the associated record details.

2. Why is this asked in interviews?

Companies like Microsoft and Amazon ask this to evaluate a candidate's basic data retrieval skills. It tests your ability to perform Joins and use Aggregate Functions like MAX() or window functions. It's a classic example of a Database interview pattern where you must filter records based on a grouped calculation.

3. Algorithmic pattern used

This problem follows the Grouping and Subquery or Window Function pattern.

• Method 1: Use a subquery to find the (departmentId, MAX(salary)) pairs and then join this result back to the original Employee and Department tables to get names.
• Method 2: Use the RANK() or DENSE_RANK() window function to assign a rank to each employee within their department based on salary, and then filter for rank = 1.

4. Example explanation

Employee Table: (Joe, 70000, 1), (Jim, 90000, 1), (Max, 90000, 2). Department Table: (1, IT), (2, Sales).

1. In IT (Dept 1), the max salary is 90,000 (Jim).
2. In Sales (Dept 2), the max salary is 90,000 (Max). Result: (IT, Jim, 90000), (Sales, Max, 90000).

5. Common mistakes candidates make

• Returning only one employee: If two employees in the same department tie for the highest salary, both must be returned. Using LIMIT 1 or a simple MAX() without a join/rank often misses ties.
• Incorrect Join: Joining on the wrong columns or forgetting to join the Department table to get the department name.
• Performance: Using correlated subqueries which can be significantly slower than a single join or window function.

6. Interview preparation tip

Master the difference between RANK(), DENSE_RANK(), and ROW_NUMBER(). For problems involving ties (like "highest salary"), RANK() or DENSE_RANK() are usually the correct choice because they assign the same value to equal inputs.