Briefly answer the following questions:
1. In the context of query optimization, what is an SQL query block?
2. Define the term reduction factor.
3. Describe a situation in which projection should precede selection in processing a project-select query, and describe a situation where the opposite processing order is better. (Assume that duplicate elimination for projection is done via sorting.)
4. If there are unclustered (secondary) B+ tree indexes on both R.a and S.b, the join R ⪻⪼a=bS could be processed by doing a sort-merge type of join-without doing any sorting-by using these indexes.
(a) Would this be a good idea if R and S each has only one tuple per page or would it be better to ignore the indexes and sort R and S? Explain.
(b) What if R and S each have many tuples per page? Again, explain.
5. Explain the role of interesting orders in the System R optimizer.