💼 SQL Detective Mode: Employees Earning More Than Their Managers

🧩 Problem Overview

In relational databases, hierarchical relationships often hold subtle insights—especially when it comes to salaries. This challenge from LeetCode, 181. Employees Earning More Than Their Managers, asks us to identify employees whose earnings surpass those of their direct managers.

The table schema is simple:

Each row represents an employee, their salary, and the ID of their manager. Our goal is to return the names of employees who earn more than their managers.

🔍 SQL Strategy: Self-Join

To solve this, we use a self-join—a powerful technique where a table is joined with itself to compare rows within the same dataset.

Here’s the logic:

• Join the employee table to itself.

• Match each employee (e2) with their manager (e1) using e2.managerId = e1.id.

• Filter where e2.salary > e1.salary.

🧪 Final Query

sql

SELECT e2.name AS Employee  
FROM employee e2  
JOIN employee e1  
ON e2.managerId = e1.id  
WHERE e2.salary > e1.salary;

📊 Sample Input

✅ Output

Joe earns more than his manager Sam—so he’s the only one returned.

🧠 Takeaway

This pattern is essential for:

• Salary audits

• Organizational hierarchy validations

• Annotation logic in classification workflows

By mastering self-joins, you unlock the ability to compare hierarchical data with precision—whether you're debugging annotation pipelines or building scalable dashboards.

🔗 Related Concepts

• Self-Join vs. Subquery: When to use which

• Hierarchical data modeling in SQL

• Salary band validation using window functions