Chapter 7, Problem 83C

Program Plan Intro

Grouping Rows:

SQL contains “GROUP BY” clause in order to group rows by common data. Though it is very powerful feature, it is hard to understand.

Syntax:

 SELECT column_Name1 FROM table_Name GROUP BY column_Name2;

Example: Consider a table “student” contains two columns “student_Name” and “Department”. “GROUP BY” clause is used when there is a need to get the number of students from each department. The query for this scenario is given as follows.

SELECT department, COUNT (department) FROM student GROUP BY department;

When the above query is executed, number of students from each department will be displayed.

Aggregate Functions:

SQL has some built-in functions and they are called as aggregate functions. SQL contains five built-in functions. They are:

• SUM – This function is used to add values from the particular column.
  • Syntax: SELECT SUM(column_Name) FROM table_Name;
• COUNT – This is used to count the number of rows for the particular column.
  • Syntax: SELECT COUNT(column_Name) FROM table_Name;
• MAX – This function is used to get the maximum value from the column.
  • Syntax: SELECT MAX(column_Name) FROM table_Name;
• MIN – This function is used to get the minimum value from the column.
  • Syntax: SELECT MIN(column_Name) FROM table_Name;
• AVG – This function is used to get the average of all the values from the column.
  • Syntax: SELECT AVG(column_Name) FROM table_Name;