Implementing Relational Operations
•We will consider how to implement:
–Selection  (     )    Selects a subset of rows from relation.
–Projection  (     )   Deletes unwanted columns from relation.
–Join  (        )  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.
–Aggregation  (SUM, MIN, etc.) and GROUP BY