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Relational Algebra Quiz

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Questions and Answers

What is the main function of filters in relational algebra?

To filter attributes/columns of a resulting relation (correct)

To aggregate values in a relation

To sort tuples in a relation

To combine multiple relations

What is a characteristic of relational algebra?

Commutative and procedural

Non-commutative and procedural (correct)

Commutative and declarative

Non-commutative and declarative

What is the purpose of the 'select' clause in relational algebra?

To combine multiple relations

To project specific attributes from a relation (correct)

To filter out tuples from a relation

To sort tuples in a relation

What is the notation for the select operation in relational algebra?

σcondition(relation) Signup and view all the answers

What is the result of applying the select operation to a relation?

A relation with less attributes or tuples than the original Signup and view all the answers

What is the purpose of the projection operation in relational algebra?

To project specific attributes from a relation Signup and view all the answers

What is an example of a query in relational algebra?

Show all first and last names of employees. Signup and view all the answers

What is the input to relational algebra operations?

Relations Signup and view all the answers

What is the symbol used to represent the selection operation in relational algebra?

σ Signup and view all the answers

What is the purpose of the 'where' clause in relational algebra?

To filter tuples based on a condition Signup and view all the answers

What is the result of the selection operation on a relation?

A relation with the same number of attributes but less tuples Signup and view all the answers

What is the purpose of the rename operation in relational algebra?

To rename attributes in a relation Signup and view all the answers

What is the notation for the selection operation that shows all employees who belong to department number 5?

σdepartment=5 Signup and view all the answers

What is the combination of operations that normally happens in relational algebra?

Selection and projection Signup and view all the answers

Study Notes

Relational Algebra

Relational algebra is a procedural language that represents a query in a mathematical way.
Relations are the inputs, and resulting relations are the outputs.

Select Operation (σ)

The select operation filters the tuples of a resulting relation R based on the condition provided.
It is commutative.
Example: σcondition(relation)
Example 1: Show all employees who belong to department number 5. σdepartment=5(employee)
Example 2: Show all employees whose monthly salary is above Php30,000 and belong to department 3, 4, and 5. σsalary > 30000 and department >=3 and department

Project Operation (π)

The project operation filters the attributes/columns of a resulting relation R based on the attributes listed.
It is not entirely commutative, but proper use of projection makes it commutative.
Example: πattributes(relation)
Example: Show all first and last names of employees. πfirstname, lastname(employee)
Example 2: Show all last names, department numbers, and monthly salaries of employees. πlastname, department, salary(employee)