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Relational Algebra Example Queries: Recap, Operators, and Banking Enterprise Schema

This learning session covers a recap on the operators of relational algebra and explores example queries using the banking enterprise schema.

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Relational Algebra Example Queries: Recap, Operators, and Banking Enterprise Schema

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  1. Session 3 Welcome: To session 3-the fourth learning sequence “Relational algebra “ Recap : In the previous learning sequences, we discussed the four operators of relational algebra. Present learning: We shall explore the following topic: - Example Queries

  2. Relational Algebra

  3. Relational Algebra • A basic expression in the relational algebra consists of either one of the following: • A relation in the database • A constant relation

  4. Relational Algebra Let E1 and E2 be relational-algebra expressions; the following are relational-algebra expressions: E1 E2 E1  E2 E1 - E2 E1 x E2 p (E1), P is a predicate on attributes in E1 s(E1), S is a list consisting of some of the attributes in E1 x(E1), x is the new name for the result of E1 The assignment operation ()

  5. Relational Schema for the Banking Enterprise branch (branch-name, branch-city, assets) customer (customer-name, customer-street, customer-only) account (account-number, branch-name, balance) loan (loan-number, branch-name, amount) depositor (customer-name, account-number) borrower (customer-name, loan-number)

  6. Example Queries Find all loans of over $1200. amount> 1200 (loan) • Find the loan number for each loan of an amount greater than $1200. loan-number (amount> 1200 (loan))

  7. Example Queries Find the names of all customers who have a loan, an account, or both, from the bank. customer-name (borrower)  customer-name (depositor) • Find the names of all customers who have a loan and an account at bank. customer-name (borrower)  customer-name (depositor)

  8. Find the names of all customers who have a loan at the Perryridge branch. Example Queries customer-name (branch-name=“Perryridge” (borrower.loan-number = loan.loan-number(borrower x loan))) • Find the names of all customers who have a loan at the Perryridge branch but do not have an account at any branch of the bank. customer-name (branch-name = “Perryridge” (borrower.loan-number = loan.loan-number(borrower x loan))) – customer-name(depositor)

  9. Find the names of all customers who have a loan at the Perryridge branch. Example Queries • Query 1customer-name(branch-name = “Perryridge”( borrower.loan-number = loan.loan-number(borrower x loan)))  Query 2 customer-name(loan.loan-number = borrower.loan-number( (branch-name = “Perryridge”(loan)) x borrower))

  10. Find the largest account balance Rename account relation as d The query is: Example Queries balance(account) - account.balance (account.balance < d.balance(account x rd (account)))

  11. Relational Algebra Summary: In this learning sequence, we discussed some example queries.

  12. END

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