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.

d. use a mixture of external and internal links

explanation:

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