Consider the set of relations shown below and the SQL query that follows. Students: (Roll_number, Name,…

Question

Consider the set of relations shown below and the SQL query that follows.

Students: (Roll_number, Name, Date_of_birth)
  Courses: (Course number, Course_name, Instructor)
  Grades: (Roll_number, Course_number, Grade)

 select distinct Name
         from Students, Courses, Grades
         where Students. Roll_number = Grades.Roll_number
              and Courses.Instructor = Korth
              and Courses.Course_number = Grades.Course_number
              and Grades.grade = A

Which of the following sets is computed by the above query?

Accepted Answer

Correct answer: C — Explanation: What the query returns and why. The FROM clause lists Students, Courses, and Grades and the WHERE conditions Students.Roll_number = Grades.Roll_number and Courses.Course_number = Grades.Course_number link the three tables so each result row corresponds to a particular student-course-grade combination. The condition Courses.Instructor = Korth restricts rows to courses taught by Korth, and Grades.grade = A restricts to rows where the student got an A in that course. select distinct Name returns each qualifying student name once, even if a student has multiple A grades in Korth’s courses. Because the query finds matching rows (student, course taught by Korth, grade A), a student appears if they have at least one A in a course taught by Korth. The query does not check that the student has A in every course taught by Korth. Note: In real SQL the literals should be quoted, e.g. Courses.Instructor = 'Korth' and Grades.grade = 'A'.

Answer

A. Names of students who have got an A grade in all courses taught by Korth

Answer

B. Names of students who have got an A grade in all courses

Answer

C. Names of students who have got an A grade in at least one of the courses taught by Korth

Answer

D. None of the above

Consider the set of relations shown below and the SQL query that follows.…