GATE CSE 2004 | Relational Algebra Question 24 | Database Management System

GATE CSE 2004

MCQ (Single Correct Answer)

-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?

$$\prod\nolimits_D {\left( {{r_2}} \right)} - \prod\nolimits_C {\left( {{r_1}} \right)} $$

$$\prod\nolimits_C {\left( {{r_1}} \right)} - \prod\nolimits_D {\left( {{r_2}} \right)} $$

$$\prod\nolimits_D {\left( {{r_1}{ \Join _{C \ne D}}{r_2}} \right)} $$

$$\prod\nolimits_C {\left( {{r_1}{ \Join _{C = D}}{r_2}} \right)} $$

GATE CSE 2003

MCQ (Single Correct Answer)

-0.3

Consider the following SQL query:

Select distinct a₁, a₂, ..., a_n 

From r₁, r₂, ..., r_m 

Where P;

For an arbitrary predicate P, this query is equivalent to which of the following relational algebra expressions?

$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \times {r_2} \times .... \times {r_m}} \right)$$

$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \Join {r_2} \Join .... \Join {r_m}} \right)$$

$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \cup {r_2} \cup .... \cup {r_m}} \right)$$

$$\prod\limits_{{a_1},{a_2},....,{a_n}} {{\sigma _p}} \left( {{r_1} \cap {r_2} \cap .... \cap {r_m}} \right)$$

GATE CSE 2002

MCQ (Single Correct Answer)

-0.3

With regard to the expressive power of the formal relational query languages, which of the following statements is true?

Relational algebra is more powerful than relational calculus.

Relational algebra has the same power as relational calculus.

Relational algebra has the same power as safe relational calculus.

None of the above

GATE CSE 2000

MCQ (Single Correct Answer)

-0.3

Given the relations

employee (name, salary, deptno), and
department (deptno, deptname, address)

Which of the following queries cannot be expressed using the basic relational algebra operations $$\left(\sigma, \pi,\times ,\Join, \cup, \cap,-\right)$$?

Department address of every employee

Employees whose name is the same as their department name

The sum of all employee’s salaries

All employees of a given department

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