ECE356 Lecture Notes - Lecture 4: Glossary Of Ancient Roman Religion, Database Server, Mcgraw-Hill Education

• School: University of Waterloo
• Department: Electrical and Computer Engineering
• Course: ECE356
• Professor: Zarnett

Document Summary

Lecture 4 relational query languages & sql, continued. When we left o we had covered the operations of selection, projection and union. Now we will continue with set di erence, cartesian product, and rename, followed by the shortcut operations. The set di erence operation works more or less as you would expect: it takes a relation and removes from it any tuples that are in the second relation. After taking away things we do not want, then we are left with the things we do want. Its input is therefore two relations and it produces a new relation as its output. The mathematical symbol is (the minus or subtraction operator). The notation is then r1 r2 where r1 and r2 are relations. This produces a relation r3 that contains all tuples in r1 that are not in r2. It is possible to chain the subtraction operators, but like regular mathematical subtraction, it does not commute: the order matters a lot.