Consider the relational schema below: Students(sid: integer, sname: string, major: string) Courses(cid: integer, cname: string, hours: integer) Enrollment(sid: integer, cid: integer, grade: real) Write a relational algebra expression that satisfies this query? Find the distinct names of all students that take at least three courses and major in "Philosophy".

Solution :

Here, we need to perform JOIN operation of the students and registration.

Use NATURAL JOIN operator and so no need to specify Join condition.

Also we need to selection operator tp select only those course whose major in "philosophy".

Finally we projection operator π to project only distinct students name who took at least three courses.

i was actually wondering the same thing but i've tried and i don't think you can. i think once you set it up then that's what it stays as. sorry ; -;