1. 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 - Example Queries

2. 2 Relational Algebra

3. uA basic expression in the relational algebra consists of either one of the following: wA relation in the database wA constant relation

4. Relational Algebra uLet E 1 and E 2 be relational-algebra expressions; the following are relational-algebra expressions: wE 1  E 2 wE1  E2 wE 1 - E 2 wE 1 x E 2 w  p (E 1 ), P is a predicate on attributes in E 1 w  s (E 1 ), S is a list consisting of some of the attributes in E 1 w  x (E 1 ), x is the new name for the result of E 1 wThe assignment operation (  )

5. Relational Schema for the Banking Enterprise ubranch (branch-name, branch-city, assets) ucustomer (customer-name, customer-street, customer-only) uaccount (account-number, branch-name, balance) uloan (loan-number, branch-name, amount) udepositor (customer-name, account-number) uborrower (customer-name, loan-number)

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

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

8. Example Queries uFind the names of all customers who have a loan at the Perryridge branch. n 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 )  customer-name (  branch-name=“Perryridge ” (  borrower.loan-number = loan.loan-number (borrower x loan)))

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

10. Example Queries Find the largest account balance uRename account relation as d uThe query is:  balance (account) -  account.balance (  account.balance < d.balance (account x  d (account)))

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

12. 12 END