Q. Consider the relation "enrolled(student, course)" in which (student, course) is the primary key, and the relation "paid(student, amount)" where student is the primary key. Assume no null values and no foreign keys or integrity constraints. Given the following four queries:

Query1: select student from enrolled where
student in (select student from paid)
Query2: select student from paid where
student in (select student from enrolled)
Query3: select E.student from enrolled E, paid P
where E.student = P.student
Query4: select student from paid where exists
(select * from enrolled where enrolled.student
= paid.student)

Which one of the following statements is correct?

View solution

Q. The following table has two attributes A and C where A is the primary key and C is the foreign key referencing A with on-delete cascade.

A C
-----
2 4
3 4
4 3
5 2
7 2
9 5
6 4

The set of all tuples that must be additionally deleted to preserve referential integrity when the tuple (2,4) is deleted is:

View solution

Q. The relation book (title, price) contains the titles and prices of different books. Assuming that no two books have the same price, what does the following SQL query list?

select title
from book as B
where (select count(*)
from book as T
where T.price > B.price) < 5

View solution

Q. Consider the following relation schema pertaining to a students database:

Student (rollno, name, address)
Enroll (rollno, courseno, coursename)

where the primary keys are rollno,courseno. The number of tuples in the Student and Enroll tables are 120 and 8 respectively. What are the maximum and minimum number of tuples that can be present in (Student * Enroll), where '*' denotes natural join ?

View solution

Q. The employee information in a company is stored in the relation
Employee (name, sex, salary, deptName)
(name is primary key )
Consider the following SQL query

select deptName
from Employee
where sex = 'M'
group by deptName
having avg (salary) > (select avg (salary) from Employee)

It returns the names of the department in which

View solution

Q. 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?

View solution

Q. Given relations r(w, x) and s(y, z), the result of

SELECT DISTINCT w, x
FROM r, s

is guaranteed to be same as r, provided

View solution

Q. In SQL, relations can contain null values, and comparisons with null values are treated as unknown. Suppose all comparisons with a null value are treated as false. Which of the following pairs is not equivalent?

View solution

Q. Consider the following three table to store student enrollements in different courses.

Student(EnrollNo, Name)
Course(CourseID, Name)
EnrollMents(EnrollNo, CourseID)
(EnrollNo,CourseID are primary keys)

What does the following query do?

SELECT S.Name
FROM Student S, Course C, Enrollments E
WHERE S.EnrollNo = E.EnrollNo AND
C.Name = "DBMS" AND
E.CourseID = C.CourseID AND
S.EnrollNo IN
(SELECT S2.EnrollNo
FROM Student S2, Course C2, Enrollments E2
WHERE S2.EnrollNo = E2.EnrollNo AND
E2.CourseID = C2.CourseID
C2.Name = "OS")

View solution

Q. Consider the following Employee table

ID salary DeptName
1 10000 EC
2 40000 EC
3 30000 CS
4 40000 ME
5 50000 ME
6 60000 ME
7 70000 CS

How many rows are there in the result of following query?

SELECT E.ID
FROM Employee E
WHERE EXISTS (SELECT E2.salary
FROM Employee E2
WHERE E2.DeptName = 'CS'
AND E.salary > E2.salary)

View solution

Q. Select operation in SQL is equivalent to

View solution

Q. Consider the following relation

Cinema (theater, address, capacity)

Which of the following options will be needed at the end of the SQL query

SELECT P1. address
FROM Cinema P1

Such that it always finds the addresses of theaters with maximum capacity?

View solution

Q. A company maintains records of sales made by its salespersons and pays them commission based on each individual's total sales made in a year. This data is maintained in a table with following schema:

salesinfo = (salespersonid, totalsales, commission)
In a certain year, due to better business results, the company decides to further reward its salespersons by enhancing the commission paid to them as per the following formula:
If commission < = 50000, enhance it by 2% If 50000 < commission < = 100000, enhance it by 4% If commission > 100000, enhance it by 6%

The IT staff has written three different SQL scripts to calculate enhancement for each slab, each of these scripts is to run as a separate transaction as follows:

 T1
Update salesinfo
Set commission = commission * 1.02
Where commission < = 50000;
 
 T2
Update salesinfo
Set commission = commission * 1.04
Where commission > 50000 and commission is < = 100000;
 
 T3
Update salesinfo
Set commission = commission * 1.06
Where commission > 100000;

  Which of the following options of running these transactions will update the commission of all salespersons correctly?

View solution

Q. A table 'student' with schema (roll, name, hostel, marks), and another table 'hobby' with schema (roll, hobbyname) contains records as shown below:

Table: Student

ROLL NAME HOSTEL MARKS
1798 Manoj Rathod 7 95
2154 Soumic Banerjee 5 68
2369 Gumma Reddy 7 86
2581 Pradeep Pendse 6 92
2643 Suhas Kulkarni 5 78
2711 Nitin Kadam 8 72
2872 Kiran Vora 5 92
2926 Manoj Kunkalikar 5 94
2959 Hemant Karkhanis 7 88
3125 Rajesh Doshi 5 82  

Table: hobby

ROLL HOBBYNAME
1798 chess
1798 music
2154 music
2369 swimming
2581 cricket
2643 chess
2643 hockey
2711 volleyball
2872 football
2926 cricket
2959 photography
3125 music
3125 chess
The following SQL query is executed on the above tables:

select hostel
from student natural join hobby
where marks > = 75 and roll between 2000 and 3000;
Relations S and H with the same schema as those of these two tables respectively contain the same information as tuples. A new relation S’ is obtained by the following relational algebra operation: S’ = ∏hostel ((σs.roll = H.roll (σmarks > 75 and roll > 2000 and roll < 3000 (S)) X (H)) The difference between the number of rows output by the SQL statement and the number of tuples in S’ is  

View solution

Q. In an inventory management system implemented at a trading corporation, there are several tables designed to hold all the information. Amongst these, the following two tables hold information on which items are supplied by which suppliers, and which warehouse keeps which items along with the stock-level of these items. Supply = (supplierid, itemcode) Inventory = (itemcode, warehouse, stocklevel) For a specific information required by the management, following SQL query has been written

Select distinct STMP.supplierid
From Supply as STMP
Where not unique (Select ITMP.supplierid
From Inventory, Supply as ITMP
Where STMP.supplierid = ITMP.supplierid
And ITMP.itemcode = Inventory.itemcode
And Inventory.warehouse = 'Nagpur');

For the warehouse at Nagpur, this query will find all suppliers who

View solution

Q. Consider the relations r1(P, Q, R) and r2(R, S, T) with primary keys P and R respectively. The relation r1 contains 2000 tuples and r2 contains 2500 tuples. The maximum size of the join r1⋈ r2 is :

View solution

Q. Student (school-id, sch-roll-no, sname, saddress)
School (school-id, sch-name, sch-address, sch-phone)
Enrolment(school-id sch-roll-no, erollno, examname)
ExamResult(erollno, examname, marks)

What does the following SQL query output?

SELECT sch-name, COUNT (*)
FROM School C, Enrolment E, ExamResult R
WHERE E.school-id = C.school-id
AND
E.examname = R.examname AND E.erollno = R.erollno
AND
R.marks = 100 AND S.school-id IN (SELECT school-id
FROM student
GROUP BY school-id
HAVING COUNT (*) > 200)
GROUP By school-id

View solution

Q. Given the basic ER and relational models, which of the following is INCORRECT?

View solution

Q. Consider a join (relation algebra) between relations r(R)and s(S) using the nested loop method. There are 3 buffers each of size equal to disk block size, out of which one buffer is reserved for intermediate results. Assuming size(r(R)) < size(s(S)), the join will have fewer number of disk block accesses if

View solution

Q. Let E1 and E2 be two entities in an E/R diagram with simple single-valued attributes. R1 and R2 are two relationships between E1 and E2, where R1 is one-to-many and R2 is many-to-many. R1 and R2 do not have any attributes of their own. What is the minimum number of tables required to represent this situation in the relational model?

View solution