What restrictions apply to the use of the aggregate functions within the SELECT statement? How do nulls affect the aggregate functions?

What is the difference between a subquery and a join? Under what circumstances would you not be able to use a subquery?

What is the result of an attempt to add, subtract, multiply, or divide two number fields, one of which contains a null value?

Explain why the two following commands produce different results.

SELECT DISTINCT COUNT (V_CODE) FROM PRODUCT;

SELECT COUNT (DISTINCT V_CODE) FROM PRODUCT;

Consider the relation instance EXM (Student, Subject, Rank). The meaning of an

EXM tuple is that a specified student examined in a specified subject achieves a specified rank in the class. Further, no two students obtain the same rank in the same subject.

EXA

Student	Subject	Rank
McGrady	Math	3
Howard	Math	4
McGrady	English	2
Jackson	English	1
Yao	Math	1
Yao	Chemistry	1
Sura	Math	2
Ward	English	3
Taylor	Chemistry	2
Taylor	Math	5
Ewing	Chemistry	3

Figure 1

What is (are) the candidate key(s) of EXM? Based on your primary key, what normal form violations exist in EXA?