Relational Algebra Flashcards
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Questions and Answers

Which of the following relational algebraic expressions is equivalent to the SQL statement SELECT * FROM Orders WHERE ord_num = '1002'?

  • σord_num = '1001'(Orders)
  • σord_num = '1003'(Orders)
  • σord_num = '1002'(Orders) (correct)
  • πord_num(Orders)

    • What type of relational algebraic operation should Ken use to find out which customers have placed orders?

    Intersection

    Which of the following SQL statements creates a natural join?

  • SELECT Customer.c_id, Orders.ord_no FROM Customer CROSS JOIN Orders;
  • SELECT * FROM Customer, Orders;
  • SELECT * FROM Customer INNER JOIN Orders ON Customer.c_id = Orders.c_id;
  • SELECT Customer.c_id, last_name, address, city, state, zip, Orders.ord_no FROM Customer, Orders WHERE Customer.c_id = Orders.c_id; (correct)

    • Which type of join keeps all rows in both relations, entering nulls in the columns with no matching values?

    <p>Full outer join</p> Signup and view all the answers

    Which relational algebraic operations will return specific columns from one single relation?

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

    Which SQL statement is equivalent to the algebraic operation σEmployee.e_id = Customer.e_id(Employee X Customer)?

    <p>SELECT Employee.<em>, Customer.</em> FROM Employee, Customer WHERE Employee.e_id=Customer.e_id;</p> Signup and view all the answers

    Which relational algebraic operations will return one or more entire rows from one single relation?

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

    Which relational algebraic operation multiplies two relations to create a new relation containing every possible pair of rows from the two original relations?

    <p>Cartesian Product</p> Signup and view all the answers

    Which SQL statement is equivalent to the algebraic operation Employee X Customer?

    <p>SELECT Employee.<em>, Customer.</em> FROM Employee, Customer;</p> Signup and view all the answers

    Which SQL statement is equivalent to the algebraic operation Employee1 ∪ Employee2?

    <p>SELECT * FROM Employee1 UNION SELECT * FROM Employee2;</p> Signup and view all the answers

    Study Notes

    Relational Algebra Concepts

    • Relational Algebra Expression: σord_num = '1002'(Orders) is equivalent to selecting orders with ord_num of '1002'.
    • Intersection: Used to find common customers who have placed orders from two distinct tables: Customers and Orders.
    • Natural Join: Achieved via SQL statement that combines Customer and Orders tables on the matching c_id field.
    • Full Outer Join: Retains all rows from both relations, inserting nulls where there are no matching values.

    Relational Algebra Operations

    • Projection: Retrieves specific columns from a single relation, focusing on particular attributes.
    • Selection: Returns one or more complete rows from a single relation based on specified criteria.
    • Cartesian Product: Combines two relations to produce a new relation with all possible pairs of rows from the original tables.

    SQL Equivalents of Algebraic Operations

    • Join Operation: σEmployee.e_id = Customer.e_id(Employee X Customer) corresponds to selecting rows in SQL where e_id matches in both Employee and Customer tables.
    • Equivalent SQL for Cartesian Product: SELECT Employee.*, Customer.* FROM Employee, Customer; represents the Cartesian product of Employee and Customer relation.
    • Union Operation: Employee1 ∪ Employee2 indicates a union of two different employee lists, providing a combined set of results from both.

    These points summarize essential relational algebra operations and their SQL counterparts, facilitating a clearer understanding of database queries and their respective algebraic representations.

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    Description

    Test your knowledge of relational algebra concepts with these flashcards. This quiz will help you understand the equivalence between SQL statements and relational algebra expressions. Additionally, it covers fundamental operations involving tables like Customers and Orders.

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