Relational Algebra

 Question 1
Consider the following three relations in a relational database.
$Employee(eId, Name), Brand (bId, bName), Own(eId ,bId)$
Which of the following relational algebra expressions return the set of $eIds$ who own all the brands?
MSQ
 A $\Pi _{eId}(\Pi _{eId,bId}(Own)/\Pi _{bId}(Brand))$ B $\Pi _{eId}(Own)-\Pi _{eId}\left ((\Pi _{eId}(Own) \times \Pi _{bId}(Brand) )-\Pi _{eId,bId}(Own) \right )$ C $\Pi _{eId}(\Pi _{eId,bId}(Own)/\Pi _{bId}(Own))$ D $\Pi _{eId}\left ((\Pi _{eId}(Own) \times \Pi _{bId}(Own) )/\Pi _{bId}(Brand) \right )$
GATE CSE 2022   Database Management System
Question 1 Explanation:
 Question 2
The following relation records the age of 500 employees of a company, where empNo ( indicating the employee number) is the key:

$empAge(\underline{empNo},age)$

Consider the following relational algebra expression:

$\Pi_{empNo}(empAge \Join_{(age > age1)} \rho_{empNo1,age1}(empAge))$

What does the above expression generate?
 A Employee numbers of only those employees whose age is the maximum B Employee numbers of only those employees whose age is more than the age of exactly one other employee C Employee numbers of all employees whose age is not the minimum D Employee numbers of all employees whose age is the minimum
GATE CSE 2021 SET-1   Database Management System
Question 2 Explanation:

 Question 3
Consider the following relation P(X, Y, Z), Q(X, Y, T) and R(Y, V):

How many tuples will be returned by the following relational algebra query?

 A 1 B 2 C 3 D 4
GATE CSE 2019   Database Management System
Question 3 Explanation:
 Question 4
Consider the relations r(A, B) and s(B, C), where s.B is a primary key and r.B is a foreign key referencing s.B. Consider the query
$Q:r \Join (\sigma _{B\lt 5}(s))$
Let LOJ denote the natural left outer-join operation. Assume that r and s contain no null values.
Which one of the following queries is NOT equivalent to Q?
 A $\sigma _{B \lt 5}(r\Join s)$ B $\sigma _{B\lt 5}(r LOJ s)$ C $r LOJ(\sigma _{B\lt 5}(s))$ D $\sigma _{B\lt 5}(r) LOJ s$
GATE CSE 2018   Database Management System
Question 4 Explanation:
 Question 5
Consider a database that has the relation schema CR (StudentName, CourseName). An instance of the schema CR is as given below.

The following query is made on the database

$T1\leftarrow \pi _{CourseName}(\sigma _{StudentName='SA'}(CR))$
$T2\leftarrow CR\div T1$

The number of rows in T2 is ____________.
 A 2 B 3 C 4 D 5
GATE CSE 2017 SET-1   Database Management System
Question 5 Explanation:

There are 5 questions to complete.

3 thoughts on “Relational Algebra”

1. please provide login facility, It’s an humble request because I solving quesions from last 2hr and suddenly all answers got removed’😒😒😥