SQL correct way of joining if the other parameter is null

Question

I have this code and its temporary tables so you can run it.

create table #student
(
    id int identity(1,1),
    firstname varchar(50),
    lastname varchar(50         


        

Answer 1

select s.firstname, s.lastname, q.id as not_taken_quiz_id, q.quiz_name as not_taken_quiz_name
from #student s
left join #quiz_details qd on s.id = qd.student_id
left join #quiz q on q.id <> qd.quiz_id

This will give you each student along with the quiz that they have not taken.