What are aggregate functions? What is their use? Give some examples.

• Aggregate functions work with multiple rows of table at a time and return single aggregate value.
• It is basically used to produce summarized data from our database.
• Basically there are five aggregate functions:
  – COUNT()
  – AVG()
  – MIN()
  – MAX()
  – SUM()
  
  Examples
  SELECT SUM(Total) FROM ITEM;

SELECT AVG(Marks) FROM Student;

SELECT DeptNo, MAX(Salary)
FROM Employee
GROUP BY DeptNo;