Relational Algebra
Basic operations:
- Selection ( ) Selects a subset of rows from relation.
- Projection ( ) Deletes unwanted columns from relation.
- Cross-product ( ) Allows us to combine two relations.
- Set-difference ( ) Tuples in reln. 1, but not in reln. 2.
- Union ( ? ) Tuples in reln. 1 and in reln. 2.
Additional operations:
- Intersection, join, division, renaming: Not essential, but (very!) useful.
Since each operation returns a relation, operations can be composed! (Algebra is “closed”.)