Left Outer Join: Include employees even if department not found join d in departments on e.Department equals d.Name from d in deptGroup.DefaultIfEmpty() select new { e.Name, Department = e.Department, Location = d?

Short answer: .Location?? "Not Found" }; var leftJoin = from e in employees into deptGroup Uses DefaultIfEmpty() to simulate outer join.

Example code

.Location?? "Not Found" }; var leftJoin = from e in employees
into deptGroup Uses DefaultIfEmpty() to simulate outer join.

Real-world example (ShopNest)

ShopNest maps entities to DTOs with .Select(o => new OrderSummaryDto { Id = o.Id, Total = o.Total }) so the API does not leak internal fields.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.