1
GATE CSE 2003
+2
-0.6
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)

Select distinct Name
and Courses.Instructor = 'Korth'
and Grades.grade = 'A';
Which of the following sets is computed by the above query?
A
Names of students who have got an A grade in all courses taught by Korth
B
Names of students who have got an A grade in all courses
C
Names of students who have got an A grade in at least one of the courses taught by Korth
D
None of the above
2
GATE CSE 2003
+1
-0.3
Consider the following SQL query:
Select distinct a1, a2, ..., an

From r1, r2, ..., rm

Where P; 
For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions?
A
$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \times {r_2} \times .... \times {r_m}} \right)$$
B
$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \Join {r_2} \Join .... \Join {r_m}} \right)$$
C
$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \cup {r_2} \cup .... \cup {r_m}} \right)$$
D
$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \cap {r_2} \cap .... \cap {r_m}} \right)$$
3
GATE CSE 2003
+1
-0.3
Which of the following scenarios may lead to an irrecoverable error in a database system?
A
A transaction writes a data item after it is read by an uncommitted transaction
B
A transaction reads a data item after it is read by an uncommitted transaction
C
A transaction reads a data item after it is written by a committed transaction
D
A transaction reads a data item after it is written by an uncommitted transaction
4
GATE CSE 2003
+2
-0.6
Consider three data items D1, D2, and D3, and the following execution schedule of transactions T1, T2, and T3. In the diagram, R(D) and W(D) denote the actions reading and writing the data item D respectively.

Which of the following statements is correct?

A
The schedule is serializable as T2; T3; T1
B
The schedule is serializable as T2; T1; T3
C
The schedule is serializable as T3; T2; T1
D
The schedule is not serializable
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