Relational Algebra Quiz
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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?

    <p>σcondition(relation)</p> Signup and view all the answers

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

    <p>A relation with less attributes or tuples than the original</p> Signup and view all the answers

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

    <p>To project specific attributes from a relation</p> Signup and view all the answers

    What is an example of a query in relational algebra?

    <p>Show all first and last names of employees.</p> Signup and view all the answers

    What is the input to relational algebra operations?

    <p>Relations</p> Signup and view all the answers

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

    <p>σ</p> Signup and view all the answers

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

    <p>To filter tuples based on a condition</p> Signup and view all the answers

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

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

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

    <p>To rename attributes in a relation</p> Signup and view all the answers

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

    <p>σdepartment=5</p> Signup and view all the answers

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

    <p>Selection and projection</p> 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)

    Rename Operation (⍴)

    • The rename operation renames a relation and/or its attributes.
    • Example: ⍴new_relation(new_attributes)(old_relation)
    • It is used to rename a relation and/or its attributes.

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    Related Documents

    CMSC 127 3rd Long Exam.pdf

    Description

    This quiz covers the basics of Relational Algebra, including filtering attributes and columns, procedural language, and relation inputs.

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