DBMS GATE Questions 2019

In this article you will get DBMS GATE Questions 2019 with answers.

1. Which one of the following statements is NOT correct about the B+ tree data structure used for creating an index of a relational database table?

a. Each leaf node has a pointer to the next leaf node
b. Non-leaf nodes have pointers to data records
c. B+ Tree is a height-balanced tree
d. Key values in each node are kept in sorted order

Answer : b)


2. Consider the following two statements about database transaction schedules:

I. Strict two-phase locking protocol generates conflict serializable schedules that are also recoverable.
II. Timestamp-ordering concurrency control protocol with Thomas Write Rule can generate view serializable schedules that are not conflict serializable.

Which of the above statements is/are TRUE? 

a. Both I and II
b. Neither I nor II
c. II only
d. I only

Answer: a)


3. Consider the following relations P(X,Y,Z), Q(X,Y,T) and R(Y,V).

How many tuples will be returned by the following relational algebra query? 

          ∏x(P.Y=R.Y  R.V=V2)(P × R)) - ∏x(Q.Y=R.Y  Q.T>2)(Q × R))

a. 0
b. 1
c. 2
d. 3

Answer : b)


4 . A relational database contains two tables Student and Performance as shown below:

Roll no.Student name
1Amit
2Priya
3Vinit
4Rohan
5smita

  Student  

Roll no.Student codeMarks
1A86
1B95
1C90
2A89
2C92
3C80

 Performance


The primary key of the Student table is Roll_no. For the Performance table, the columns Roll_no. and Subject_code together from the primary key. Consider the SQL query given below:

SELECT S.Student_name, sum (P.Marks)
FROM Student S, Performance P
WHERE P.Marks > 84
GROUP BY S.Student_name;

The number of rows returned by the above SQL query is _____. 

a. 0
b. 9
c. 7
d. 5

Answer : d)
DBMS |Gate-2019|


5. Let the set of functional dependencies F = {QR → S, R → P, S → Q} hold on a relation schema X = (PQRS). X is not in BCNF. Suppose X is decomposed into two schemas Y and Z, where Y = (PR) and Z = (QRS).

Consider the two statements given below.

I. Both Y and Z are in BCNF
II. Decomposition of X into Y and Z is dependency preserving and lossless

Which of the above statements is/are correct?  

a. I only
b. Neither I nor II
c. II only
d. Both I and II

Answer : c)

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