When do you use a self-join in SQL Server?

Short answer: When rows relate to other rows in the same table — classic employee/manager, find peers in same department, or compare a row to another version.

Sample solution

SELECT e.Name AS Employee, m.Name AS Manager
FROM Employees e
LEFT JOIN Employees m ON e.ManagerId = m.EmpId;

Always alias both sides clearly (e/m) — interviewers flag missing aliases.