tags:

views:

65

answers:

1
Q: 

How would I find the highest/largest of something with relation algebra, domain relational calculus and tuple relational calculus

This is part of a homework assignment. I've got several questions asking find the eid of the employee with the highest salary, or 2nd highest salary. Find the pilot that is certified for the most aircrafts. I don't have any idea on how to do it. There aren't any examples in the chapter, and google is proving less that helpful. If someone could show me how to do just one of these, it'll help a lot.

here are the tables:

Aircraft( aid: integer, aname: string, cruisingrange: integer )

Certified( eid: integer, aid: integer )

Employees( eid: integer, ename: string, salary: int )

+1  A: 

I can give you an hint in how to obtain max and min values:

think about the fact that you can join an entity over itself, now think what join criteria you could use.. and then you can use the result of the join to subtract results from your initial set of elements

EDIT: what happens if you join employers with them selves with a criteria of having first salary <= second salary?

Jack  2010-03-11 22:29:51
@Jack: +1 for teaching to fish.
Eric J.  2010-03-11 22:32:34
I can still only think of a temp variable or something. It might be a little easier if we did anything like this in class, or even if the book had covered it.
Justen  2010-03-11 22:35:12
@EDIT: ok, I understand that logic. Get everyone who doesn't have the highest one, and the set difference operator. Now I guess I just need to figure out how to write it.
Justen  2010-03-11 23:37:21

related questions

What would be the simplest way to alpha sort an array of chars in C?
Failed software development
When does ++ not produce the same results as +1?
Shortest Root to Leaf Path
Repository Pattern Implementation Experience
Algorithm to detect similar documents in python script
Separation of Concerns
Creating a java servlet web application
How do you solve the 15-puzzle with A-Star or Dijkstra's Algorithm?
Algorithm to find which numbers from a list of size n sum to another number
software Engineering documentation
What is round-robin scheduling?
What is a multitasking operating system?
How do I clip a line segment against a frustum?
How do I capitalize first letter of first name and last name in C#?
Why is quicksort better than mergesort?
Hidden Markov Models
Using Stack as Queue
Database design for a booking application e.g. hotel
What is a good algorithm for deciding whether a passed in amount can be built additively from a set of numbers?
How to identify specific digits of an integer input in C?
Interesting interview questions
Print Odd-Even numbers using signals
What is the best way to learn recursion?
Are foreign keys really necessary in a database design?