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Questions and Answers

What does the operation 'Select' do?

  • Selects all tuples that satisfy the selection condition from a relation R. (correct)
  • Selects all tuples from a database.
  • Selects tuples based on a specific attribute.
  • Selects unique tuples from a relation.

    • What is the function of the 'Project' operation?

  • Selects tuples that match certain criteria.
  • Finds the difference between two relations.
  • Produces a new relation with only some attributes of R and removes duplicate tuples. (correct)
  • Combines two relations based on a condition.

    • What does 'Theta Join' produce?

  • All combinations of tuples from R_1 and R_2 that satisfy the join condition. (correct)
  • A relation with no duplicate tuples.
  • Only those tuples where a specific attribute matches.
  • A relation that combines attributes from multiple relations.

    • What is the primary characteristic of 'Equijoin'?

    <p>Produces combinations of tuples using only equality comparisons.</p> Signup and view all the answers

    How does 'Natural Join' differ from 'Equijoin'?

    <p>Natural Join does not include the join attributes of R_2 in the resulting relation.</p> Signup and view all the answers

    What does the 'Union' operation do?

    <p>Produces a relation including all tuples in R_1 or R_2, or both.</p> Signup and view all the answers

    What is the 'Intersection' operation used for?

    <p>Including all tuples in both R_1 and R_2.</p> Signup and view all the answers

    What does the 'Difference' operation yield?

    <p>All tuples from R_1 that are not in R_2.</p> Signup and view all the answers

    What kind of relations does 'Cartesian Product' produce?

    <p>Relations with attributes of R_1 and R_2 and includes all possible combinations of tuples.</p> Signup and view all the answers

    What is the purpose of the 'Division' operation?

    <p>To produce a relation R(X) that includes all tuples t[X] in R_1(Z) that appear in R_1 with every tuple from R_2(Y).</p> Signup and view all the answers

    Study Notes

    Relational Algebra Operations

    • Select: Filters tuples from relation R based on a specified condition, retaining only those that meet the criteria.

    • Project: Creates a new relation containing specific attributes from relation R while eliminating duplicate tuples.

    • Theta Join: Generates all possible pairs of tuples from relations R_1 and R_2 that fulfill a designated join condition.

    • Equijoin: Similar to theta join, but only includes pairs of tuples from R_1 and R_2 based on equality comparisons in the join condition.

    • Natural Join: A special type of equijoin that automatically combines tuples from R_1 and R_2 while excluding duplicate join attributes. Duplicate attribute names do not need specification.

    • Union: Combines tuples from R_1 and R_2, including all unique tuples from both. Relations R_1 and R_2 must be compatible in terms of attributes for this operation.

    • Intersection: Results in a relation containing only tuples that appear in both R_1 and R_2. Both relations must be union compatible.

    • Difference: Produces a relation containing tuples from R_1 that are absent in R_2. This operation requires R_1 and R_2 to be union compatible.

    • Cartesian Product: Forms a new relation by merging attributes from R_1 and R_2, resulting in all possible combinations of their tuples.

    • Division: Creates relation R(X) consisting of all tuples t[X] from R_1(Z) that are associated with every tuple in R_2(Y), where Z is the union of X and Y.

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