Oracle Database Interview Question:

How To Test NULL Values?

Submitted by: Administrator

There ate two special comparison operators you can use on NULL values:

► "variable IS NULL" - Returns TRUE if the variable value is NULL.
► "variable IS NOT NULL" - Return TRUE if the variable value is not NULL.

The following sample script shows you examples of comparing NULL values:

DECLARE
next_task CHAR(80);
BEGIN
next_task := NULL;

IF next_task IS NOT NULL THEN
DBMS_OUTPUT.PUT_LINE('I am busy.');
ELSE
DBMS_OUTPUT.PUT_LINE('I am free.');
END IF;

IF next_task IS NULL THEN
NULL;
ELSE
DBMS_OUTPUT.PUT_LINE('... working on ' || next_task);
END IF;
END;

Note that "variable = NULL" is not a valid operation. This script should print this:

I am free.

Submitted by: Administrator