DBMS |Gate-2011| Database Management System
1. Consider a relational table with a single record for each registered student with the following attributes. [GATE – 2011]
1. Registration_Num: Unique registration number
of each registered student
2. UID: Unique identity number, unique at the
national level for each citizen
3. BankAccount_Num: Unique account number at
the bank. A student can have multiple accounts
or join accounts. This attribute stores the
primary account number.
4. Name: Name of the student
5. Hostel_Room: Room number of the hostel
Which one of the following option is INCORRECT?
a. BankAccount_Num is a candidate key
b. Registration_Num can be a primary key
c. UID is a candidate key if all students are from the same country
d. If S is a superkey such that S∩UID is NULL then S∪UID is also a superkey
Answer : a)
2. Consider a relational table r with sufficient number of records, having attributes A1, A2,…, An and let 1 <= p <= n. Two queries Q1 and Q2 are given below.
The database can be configured to do ordered indexing on Ap or hashing on Ap. Which of the following statements is TRUE? [GATE – 2011]
a. Ordered indexing will always outperform hashing for both queries
b. Hashing will always outperform ordered indexing for both queries
c. Hashing will outperform ordered indexing on Q1, but not on Q2
d. Hashing will outperform ordered indexing on Q2, but not on Q1.
Answer : c)
3. Database table by name Loan_Records is given below.
Borrower Bank_Manager Loan_Amount
Ramesh Sunderajan 10000.00
Suresh Ramgopal 5000.00
Mahesh Sunderajan 7000.00
What is the output of the following SQL query? [GATE – 2011]
SELECT Count(*)
FROM ( ( SELECT Borrower, Bank_Manager
FROM Loan_Records) AS S
NATURAL JOIN ( SELECT Bank_Manager, Loan_Amount
FROM Loan_Records) AS T );
a. 3
b. 9
c. 6
d. 5
Answer : d)
4. Consider a database table T containing two columns X and Y each of type integer. After the creation of the table, one record (X=1, Y=1) is inserted in the table. Let MX and My denote the respective maximum values of X and Y among all records in the table at any point in time. Using MX and MY, new records are inserted in the table 128 times with X and Y values being MX+1, 2*MY+1 respectively. It may be noted that each time after the insertion, values of MX and MY change. What will be the output of the following SQL query after the steps mentioned above are carried out? [GATE – 2011]
SELECT Y FROM T WHERE X=7;
a. 126
b. 127
c. 255
d. 257
Answer : b)
DBMS |Gate-2011|