What Are NULL Values

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Q

What Are NULL Values? - MySQL FAQs - Introduction to SQL Basics

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A

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

2007-05-11, 5462👍, 0💬

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