MySQL Programming Question:

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!