🧠 Advanced SQL Interview Question ⚡

📊 Find pairs of employees who work in the same department and earn the same salary

Table: Employees

Columns:

employee_id, employee_name, department_id, salary

🔍 Query:

SELECT e1.employee_id AS emp1_id,
e1.employee_name AS emp1_name,
e2.employee_id AS emp2_id,
e2.employee_name AS emp2_name,
e1.department_id,
e1.salary
FROM Employees e1
JOIN Employees e2
ON e1.department_id = e2.department_id
AND e1.salary = e2.salary
AND e1.employee_id < e2.employee_id;

🎯 Why this question matters:

✅ Tests self joins deeply
✅ Evaluates logical thinking in SQL
✅ Commonly asked in advanced interview rounds

🚀 Pro Tip:

Self joins are extremely useful for comparing rows within the same table without using loops.

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