What Happens If NULL Values Are Involved in Expressions

Q

What Happens If NULL Values Are Involved in Expressions? - MySQL FAQs - Introduction to SQL Basics

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A

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!

2007-05-11, 4511👍, 0💬