what is difference between using

1. right outer join,
2. left outer join,
3. inner join.

example :

select *from course right outer join prereq on course.course_id = prereq.course_id;

select *from course left outer join prereq on course.course_id = prereq.course_id;

select *from course inner join prereq on course.course_id = prereq.course_id;