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
B+ tree is a height-balanced tree
B
Non-leaf nodes have pointers to data records
C
Each leaf node has a pointer to the next leaf node
D
Key values in each node are kept in sorted order
2
GATE CSE 2019
MCQ (Single Correct Answer)
+1
-0.33
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
I only
C
II only
D
Neither I nor II
3
GATE CSE 2019
Numerical
+2
-0.67
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?
Your input ____
4
GATE CSE 2019
Numerical
+2
-0.67
A relational database contains two tables Student and Performance as shown below:
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 _____.
