Database Management System MCQs

6. Question

Let r be a relation instance with schema R = (A, B, C, D). We define r1 = Π A,B,C (r) and r2 = Π A,D (r ).Let s = r * r where * denotes natural join. Given that the decomposition of r into r1 and r2 is lossy, which one of the following is TRUE?

7. 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?

8. Question

Consider the following relational schema.
Students(rollno: integer, sname: string)
Courses(courseno: integer, cname: string)
Registration(rollno: integer, courseno; integer, percent: real)
Which of the following queries are equivalent to this query in English?
“Find the distinct names of all students who score more than 90% in the course
numbered 107”

9. Question

Relation R has eight attributes ABCDEFGH. Fields of R contain only atomic values.
F = {CH → G, A →BC, B →CFH, E →A, F →EG} is a set of functional dependencies (FDs) so that F+ is exactly the set of FDs that hold for R

The relation R is

10. Question

Consider the following functional dependencies in a database.
Date_of_Birth →  Age                                    Age →  Eligibility
Name  → Roll_number                                 Roll_number → Name
Course_number →  Course_name          Course_number → Instructor
(Roll_number, Course_number) →  Grade
The relation (Roll_number, Name, Date_of_birth, Age) is


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