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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.
Notes:
The query we really answer is: “List the names of all the employees, except those for which there is an employee of “SBC” with a higher or equal salary.”