Chapter 4, Problem 21TD

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.

NULL:

• Sometimes a condition occupies a column that can allow null values.
• To find rows in which a particular column contain a null value, then the SQL uses “IS NULL” operator.
• If it does not contain a null value, then the SQL uses “IS NOT NULL” operator.

Example:

The example for using “IS NULL” operator is given below:

SELECT STUDENT_ID, STUDENT_NAME FROM STUDENT WHERE STREET IS NULL;

The above query is used for selecting rows containing null values in the “STREET” column.