Find Salary Peers in the Same Department - Easy SQL Self Joins Interview Problem

Problem

Your HR team wants to flag employees who earn the same salary as a colleague in the same department. Using the employees table, find all pairs of employees in the same department with equal salaries. To avoid listing the same pair twice, only include pairs where the first employee's id is less than the second's.

Return employee1, employee2, department, and salary. Sort by salary.

Schema

employees

column	type
id	INTEGER
name	TEXT
department	TEXT
salary	NUMERIC

Sample Data

id	name	department	salary
1	Alice	Engineering	90000
2	Bob	Engineering	90000
3	Carol	Marketing	75000
4	Dave	Marketing	75000
5	Eve	Engineering	80000

Expected Output

employee1	employee2	department	salary
Carol	Dave	Marketing	75000
Alice	Bob	Engineering	90000

Explanation

Alice and Bob both earn 90000 in Engineering — they form a pair. Carol and Dave both earn 75000 in Marketing — they form a pair. Eve has no salary match in Engineering, so she does not appear.

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