Question about query builder add table without join

Hey! I am beginner at Laravel and would like to know if possible in query builder add some tables without join? For example, I have table "users" with "user_id" column and I want to add table "reg_info" with column "id". In first table we have more user ids than in second table, but I want to select student's which are registered and students which are not registered to the system. If I would join these table, then only registered students will appear. Any thoughts what to do?