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(σ(P.Y=R.Y ∧ R.V=V2)(P × R)) - ∏x(σ(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 |
| 1 | Amit |
| 2 | Priya |
| 3 | Vinit |
| 4 | Rohan |
| 5 | Smita |
Student
| Roll no. | Student code | Marks |
| 1 | A | 86 |
| 1 | B | 95 |
| 1 | C | 90 |
| 2 | A | 89 |
| 2 | C | 92 |
| 3 | C | 80 |
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)
