Relational Algebra Overview
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Questions and Answers

What is the PROJECT operation denoted by?

  • π (pi) (correct)
  • σ (sigma)
  • ρ ( rho )
  • λ (lambda)
  • What does the PROJECT operation do to the columns of a relation?

  • It renames certain columns
  • It removes certain columns and keeps the others
  • It keeps certain columns and discards the others (correct)
  • It rearranges certain columns
  • What is the main purpose of the PROJECT operation?

  • To combine two relations
  • To remove duplicate tuples from a relation
  • To select specific columns from a relation (correct)
  • To reorder the columns of a relation
  • What is the result of applying the PROJECT operation to a relation?

    <p>A relation with certain columns removed</p> Signup and view all the answers

    What is an alternative term for the PROJECT operation?

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

    What is a relation in a relational model based database?

    <p>A table in the database</p> Signup and view all the answers

    What does the term 'relationship' refer to in a relational model based database?

    <p>How two tables are connected together</p> Signup and view all the answers

    What is the main difference between relation and relationship in DBMS?

    <p>Table and connection between tables</p> Signup and view all the answers

    What is the role of a relation in a relational model based database?

    <p>To store and manage data</p> Signup and view all the answers

    What is the primary function of a relationship in a relational model based database?

    <p>To establish connections between tables</p> Signup and view all the answers

    What can be said about the number of tuples in the result of projection π(R)?

    <p>It is always less than or equal to the number of tuples in R</p> Signup and view all the answers

    What is a condition under which the number of tuples in the result of PROJECT is equal to the number of tuples in R?

    <p>If the list of attributes includes a key of R</p> Signup and view all the answers

    Is the PROJECT operation commutative?

    <p>No, the PROJECT operation is not commutative</p> Signup and view all the answers

    What is the condition under which π(π(R)) = π(R)?

    <p>π contains the attributes in</p> Signup and view all the answers

    What is the purpose of the PROJECT operation?

    <p>To select certain attributes from a relation</p> Signup and view all the answers

    What is a necessary condition for a union operation to be valid?

    <p>The relations have the same number of attributes.</p> Signup and view all the answers

    What is a requirement for relations r and s to be union-compatible?

    <p>They must have the same number of attributes.</p> Signup and view all the answers

    Which of the following is NOT a condition for a valid union operation?

    <p>The relations have the same database.</p> Signup and view all the answers

    What is the primary purpose of checking the number of attributes in a union operation?

    <p>To ensure the relations have the same number of attributes.</p> Signup and view all the answers

    Why do relations r and s need to have the same number of attributes for a valid union operation?

    <p>To ensure the union operation is valid.</p> Signup and view all the answers

    What does the INTERSECTION operation (∩) produce?

    <p>A relation with tuples that are in both R and S</p> Signup and view all the answers

    What is a requirement for the two operand relations R and S?

    <p>They must be type compatible</p> Signup and view all the answers

    What are the attribute names in the result of the INTERSECTION operation?

    <p>The same as the attribute names in R</p> Signup and view all the answers

    What is the symbol used to denote the INTERSECTION operation?

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

    What is the result of R ∩ S?

    <p>A relation with tuples that are in both R and S</p> Signup and view all the answers

    Study Notes

    Relational Algebra Overview

    • In a relational model-based database, a "relation" refers to a table, while a "relationship" refers to the connection between two tables.

    Unary Relational Operations: PROJECT

    • The PROJECT operation is denoted by π (pi) and keeps certain columns (attributes) from a relation, discarding the others.
    • Properties of PROJECT operation:
      • The number of tuples in the result of projection π(R) is always less than or equal to the number of tuples in R.
      • If the list of attributes includes a key of R, then the number of tuples in the result of PROJECT is equal to the number of tuples in R.
      • PROJECT is not commutative: π (π (R) ) = π (R) as long as contains the attributes in .

    Relational Algebra Operations from Set Theory: UNION

    • For a union operation to be valid, the following conditions must hold:
      • R and S must have the same number of attributes.

    Relational Algebra Operations from Set Theory: INTERSECTION

    • INTERSECTION is denoted by ∩.
    • The result of the operation R ∩ S is a relation that includes all tuples that are in both R and S.
    • The attribute names in the result will be the same as the attribute names in R.
    • The two operand relations R and S must be "type compatible".

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    Description

    Learn about the difference between relation and relationship in DBMS, including how they relate to tables and connections in a relational model based database.

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