What Is NULL?

NULL is a special value representing "no value" in all data types. NULL can be used on in
operations like other values. But most opertations has special rules when NULL is involved. The
tutorial exercise below shows you some examples:
SET NULL 'NULL'; -- Make sure NULL is displayed
SELECT NULL FROM DUAL;
N
-
N
U
L
L
SELECT NULL + NULL FROM DUAL;
NULL+NULL
----------
NULL
SELECT NULL + 7 FROM DUAL;
NULL+7
----------
NULL
SELECT NULL * 7 FROM DUAL;
NULL*7
----------
NULL
SELECT NULL || 'A' FROM DUAL;
N
-
A
SELECT NULL + SYSDATE FROM DUAL;
NULL+SYSD