Chapter 16, Problem 25E

a.

Explanation of Solution

Way to evaluate the query:

• Consider a situation, when only top few “K” answers to $\text{r}\left|\text{><}\right|\text{s}$ of relations “r” and “s” with an index of attribute “A” is required.
• When the join is on a foreign key of relation “r” referencing “s”,
  • An each tuple of relation “r” will join with only one tuple of relation “s”

b.

Explanation of Solution

Way to evaluate the query when a join is not on a foreign key:

• Consider a situation, when only top few “K” answers to $\text{r}\left|\text{><}\right|\text{s}$ of relations “r” and “s” with an index of attribute “B” is required