Database 1
Data Manipulation
- Prof. dr. Paul M.E. De Bra
- Dept. of Computer Science
- Eindhoven Univ. of Technology
Library Questions
- List all the authors of books of which the library has a copy that has never been borrowed.
- List all the authors of books that have never been borrowed.
- List all the authors of which no book has ever been borrowed.
Exercise 3.5g
- Find the names of all employees who earn more than every employee of “SBC”.
- The “more than every...” clause cannot be expressed directly in the relational algebra.
- For all other employees there is an employee of “SBC” earning more. This can be described using a selection on a cartesian product (of works with works).
- We then use the difference to find the correct result.
Exercise 3.5h
- Find all companies located in every city in which “SBC” is located.
- The “every city...” clause cannot be expressed directly in the relational algebra.
- For the other companies there is a city in which “SBC” is located and the other company is not.
- The cities where a company is not located are all the cities except the ones where the company is located.
- We thus need 2 times a difference in this query.
Preparation for colstruction 2
- The preparation is for colstruction 2 instead of labsession 2 because of a holiday.
- Study chapter 3 of the database book, up to and including all of section 3.2.
- In 3.2.3 additional operators are introduced that make the expression of some queries easier.
- Note that we are not going to study sections 3.3, 3.4 and 3.5.