1
GATE CSE 2004
+1
-0.3
Let R1 (A, B, C) and R2 (D, E) be two relation schema, where the primary keys are shown underlined, and let C be a foreign key in R1 referring to R2. Suppose there is no violation of the above referential integrity constraint in the corresponding relation instances r1 and r2. Which one of the following relational algebra expressions would necessarily produce an empty relation?
A
$$\prod\nolimits_D {\left( {{r_2}} \right)} - \prod\nolimits_C {\left( {{r_1}} \right)}$$
B
$$\prod\nolimits_C {\left( {{r_1}} \right)} - \prod\nolimits_D {\left( {{r_2}} \right)}$$
C
$$\prod\nolimits_D {\left( {{r_1}{ \Join _{C \ne D}}{r_2}} \right)}$$
D
$$\prod\nolimits_C {\left( {{r_1}{ \Join _{C = D}}{r_2}} \right)}$$
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 2002
+1
-0.3
With regard to the expressive power of the formal relational query languages, which of the following statements is true?
A
Relational algebra is more powerful than relational calculus.
B
Relational algebra has the same power as relational calculus.
C
Relational algebra has the same power as safe relational calculus.
D
None of the above
4
GATE CSE 2000
+1
-0.3

Given the relations

employee (name, salary, deptno), and

Which of the following queries cannot be expressed using the basic relational algebra operations $$\left(\sigma, \pi,\times ,\Join, \cup, \cap,-\right)$$?
A
B
Employees whose name is the same as their department name
C
The sum of all employee’s salaries
D
All employees of a given department
GATE CSE Subjects
Theory of Computation
Operating Systems
Algorithms
Digital Logic
Database Management System
Data Structures
Computer Networks
Software Engineering
Compiler Design
Web Technologies
General Aptitude
Discrete Mathematics
Programming Languages
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