⟩ What Happens If NULL Values Are Involved in Expressions?
If NULL values are used in expressions, the resulting values will be NULL values. In other words:
► Arithmetic expressions with NULL values result NULL values.
► Comparison expressions with NULL values result NULL values.
► Logical expressions with NULL values result NULL values.
The tutorial exercise shows you some interesting examples:
SELECT NULL + NULL FROM DUAL;
NULL
SELECT NULL + 7 FROM DUAL;
NULL
SELECT NULL * 7 FROM DUAL;
NULL
SELECT NULL = NULL FROM DUAL;
NULL
SELECT 0 < NULL FROM DUAL;
NULL
SELECT '' > NULL FROM DUAL;
NULL
SELECT NULL AND TRUE FROM DUAL;
NULL
SELECT NULL OR TRUE FROM DUAL;
1
-- This is contradicting against the rules!
