What is the third rule to normalize a database? All primary keys must be based on filtered values.
All fields in the table must be included in the primary key.
Each primary key must be based on multiple fields in the table.
Each nonkey field must relate to the entire single-field primary key.

Answer is 4
Each nonkey field must relate to the entire single-field primary key

Suppose there is a relation r(a, b, c) with a b+-tree index with search keys (a, b).1. what is the worst-case cost of finding records satisfying 10 < a < 50 using this index, in terms of the number of records n1, retrieved and the height h of the tree? 2. what is the worst-case cost of finding records satisfying 10 < a < 50 and 5 < b < 10 using this index, in terms of the number of records n2 that satisfy this selection, as well as n1 and h defined above? 3. under what conditions on n1 and n2, would the index be an efficient way of finding records satisfying the condition from part (2)?