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  1. #1
    Join Date
    Sep 2013
    Posts
    1

    Exclamation Relational Algebra Question

    Hey guys, I am studying for an Exam, and was hoping for some guidance on a particular Relational Algebra question I am not sure on.

    Scenario:

    Consider the database schema on the relations (where key attributes have been underlined):

    COURSES(Number, Faculty, CourseName)
    STUDENTS(RegNumber, Surname, FirstName, Faculty)
    EXAMS(Student, Course, Grade, Date)

    NOTE: relation EXAMS stores the registration number (attribute Student) of students that passed the exam for a given course (attribute Course is the number of course, not the name of the course), the grade and the date of the exam.

    Question:

    Formulate in relational algebra the query that retrieves for every course number in the Science faculty, the registration number and surname of students who passed the exam for such a course during the period 01/05/2010-15/05/2010.

    My Answer

    PROJECT Number, RegNumber, Surname (RESTRICT date > 30/04/2010 AND date < 16/05/2010 AND Grade > E(Courses JOIN r.number=Course Exams AND Students JOIN r.RegNumber = Student Exams))

    Do you guys think my answer is correct? If not, what should I change? Thanks

  2. #2
    Join Date
    Jan 2003
    Location
    Massachusetts
    Posts
    5,799
    Not too sure about the syntax, but one point about the RESTRICT clause, does the Date attribute include a time portion? If it does, then someone who takes and passes the exam at noon on 30/04/2010 will show up in your result set. Also, I don't see anything about the Science faculty. Lastly, since I don't know the syntax you are using, I see r.Number, and r.RegNumber, is "r" an alias for the Exams table? Does it need to be declared?

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