Tutorial 3: Relational Algebra

1
Tutorial 3 Relational Algebra
2

• Question
• We know that natural join is not a basic
  operator in relational algebra. Hence, there must
  be away to replace it with an equivalent
  expression involving only basic operators. Next
  we will see how to do this.
• Given R (A, B, C, D) and S (E, B, D), rewrite
  R S into a relational algebra expression
  involving only ?, s, and .

3

• Question
• OWNS(acc-id, cust-id)
• ACC(acc-id, balance).
• Write a relational algebra query to find the
  cust-ids of the owners of all accounts with
  balances at least 10k.

4

• Question
• OWNS(acc-id, cust-id).
• ACC(acc-id, balance).
• Write a relational algebra query to find the
  acc-id of every account whose balance is larger
  than all the accounts owned by the customer with
  cust-id C1.
• Note If your query is too complex, you can cut
  it into multiple steps by using the assignment
  operator ?.
• For example, A ?scust-idC1(OWNS) defines a table
  A that is the result of the selection. Then, you
  can use A directly in the subsequent expressions.
  For example, ?acc-id (A) projects A onto column
  acc-id.

5

• Question
• DEPOSIT(acc-id, cust-id, amount).
• Write a relational algebra query to find all the
  cust-id of all those customers that touched all
  the accounts touched by the customer with cust-id
  1.
• Touch means depositing into the account.