Lecture 4 - Aggregate Functions

Question 1

What are aggregate functions?

Answer 1

Statistical summaries over a group of tuples

Question 2

Examples of aggregate functions?

Answer 2

COUNT(X) , SUM(X) , MAX(X) , AVG(X) , COR (X,Y)

Question 3

What is special about COUNT(X)?

Answer 3

It doesn’t count NULL values.

Question 4

What is a UDA?

Answer 4

User DEfine Aggregate

• definiting your own aggregate function

Question 5

Example of aggregate function.

Answer 5

SELECT MAX (Salary) AS Highest_Sal,
MIN (Salary) AS Lowest_Sal,
AVG (Salary) AS Average_Sal
FROM EMPLOYEE
WHERE DNO = 5;