# 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?

Answer

##### 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?

Answer

##### 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”

Answer

##### 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

Answer

##### 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

Answer