MySQL Programming Interview Question:

What Are NULL Values?

Submitted by: Administrator

NULL is a special value that represents no value. Here are basic rules about NULL values:

► NULL presents no value.
► NULL is not the same as an empty string ''.
► NULL is not the same as a zero value 0.
► NULL can be used as any data type.
► NULL should not be used in any comparison options.
► NULL has its own equality operator "IS".
► NULL has its own not-equality operator "IS NOT".

The tutorial exercise shows you some interesting examples:

SELECT 0 IS NULL FROM DUAL;
0

SELECT 0 IS NOT NULL FROM DUAL;
1

SELECT '' IS NULL FROM DUAL;
0

SELECT '' IS NOT NULL FROM DUAL;
1

SELECT NULL IS NULL FROM DUAL;
1

SELECT NULL IS NOT NULL FROM DUAL;
0
Submitted by: Administrator