Chapter 4, Problem 20TD

Program Plan Intro

“SELECT” command:

The “SELECT” command is used to retrieve data in a database.

Syntax for selecting values from the table is as follows:

SELECT STUDENT_ID FROM STUDENT;

• The given query is used to display each student ID from “STUDENT” table.

“ORDER BY” Clause:

• User can sort the data in specific order using “ORDER BY” clause.
• The column on which to sort data is called a sort key or a simple key.
• To sort the output, use an “ORDER BY” clause followed by the sort key.
• If the user does not indicate a sort order, the output displayed in default order that is ascending order.

Example:

The example for “ORDER BY” clause is given below:

SELECT STUDENT_ID, STUDENT_NAME, STUDENT_CREDIT FROM STUDENT ORDER BY STUDENT_CREDIT;

 The above query is used to list student ID, name and credit for each student with ascending order of student credit using an “ORDER BY” clause.

• From the given query, the sort key is “STUDENT_CREDIT”. So, the rows are sorted in ascending order by “STUDENT_CREDIT”.

“GROUP BY” Clause:

• User can group the data using “GROUP BY” clause.
• This clause allows the user to group data on a specific column and then computes statistics when user preferred.

Example:

The example for “GROUP BY” clause is given below:

SELECT CUSTOMER_NAME, SUM(AMOUNT) FROM CUSTOMERS GROUP BY CUSTOMER_NAME;

The above query is used to list the customer name and the sum of amount using “GROUP BY” clause.

“HAVING” Clause:

• The “HAVING” clause is used to restrict the groups that are included.
  • This restriction does not apply to individual rows but relatively apply to groups.

Example:

The example for “HAVING” clause is given below:

SELECT STUDENT_ID, NAME, AGE, ADDRESS, TOTAL_MARK FROM STUDENTS GROUP BY AGE HAVING COUNT(AGE) >= 10;

• The above query is used to display a record for a similar age count that would be more than or equal to “10”.