What Happens If NULL Values Are Involved in Expressions

Home > MySQL > SQL

Q

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

✍: FYIcenter.com

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, 5448👍, 0💬

How To Enter Numeric Values as HEX Numbers
How To Enter Numeric Values as HEX Numbers? - MySQL FAQs - Introduction to SQL Basics If you want to enter numeric values as HEX numbers, you can quote HEX numbers with single quotes and a prefix of (X), or just prefix HEX numbers with (0x). A HEX number string will be automatically converted into a... 2007-05-11, 9822👍, 0💬

How To Enter Boolean Values in SQL Statements
How To Enter Boolean Values in SQL Statements? - MySQL FAQs - Introduction to SQL Basics If you want to enter Boolean values in SQL statements, you use (TRUE), (FALSE), (true), or (false). Here are some good examples: SELECT TRUE, true, FALSE, false FROM DUAL; +------+------+-------+------- +| TRUE ... 2007-05-11, 9662👍, 0💬

How To Enter Characters as HEX Numbers
How To Enter Characters as HEX Numbers? - MySQL FAQs - Introduction to SQL Basics If you want to enter characters as HEX numbers, you can quote HEX numbers with single quotes and a prefix of (X), or just prefix HEX numbers with (0x). A HEX number string will be automatically converted into a charact... 2007-05-11, 7535👍, 0💬

How To Convert Numeric Values to Character Strings
How To Convert Numeric Values to Character Strings? - MySQL FAQs - Introduction to SQL Basics You can convert numeric values to character strings by using the CAST(value AS CHAR) function as shown in the following examples: SELECT CAST(4123.45700 AS CHAR) FROM DUAL; 4123.45700 -- How to get rid of t... 2007-05-11, 5819👍, 0💬

What Happens If NULL Values Are Involved in Expressions
What Happens If NULL Values Are Involved in Expressions? - MySQL FAQs - Introduction to SQL Basics 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 res... 2007-05-11, 5449👍, 0💬

What Are NULL Values
What Are NULL Values? - MySQL FAQs - Introduction to SQL Basics 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. NUL... 2007-05-11, 5445👍, 0💬

How To Use Regular Expression in Pattern Match Conditions
How To Use Regular Expression in Pattern Match Conditions? - MySQL FAQs - Introduction to SQL Basics If you have a pattern that is too complex for LIKE to handle, you can use the regular expression pattern condition: REGEXP. The following tutorial exercise provides you some good examples: SELECT 'FY... 2007-05-11, 5348👍, 0💬

How To Convert Character Strings to Numeric Values
How To Convert Character Strings to Numeric Values? - MySQL FAQs - Introduction to SQL Basics You can convert character strings to numeric values by using the CAST(string AS DECIMAL) or CAST(string AS SIGNED INTEGER) function as shown in the following examples: SELECT CAST('4123.45700' AS DECIMAL) F... 2007-05-11, 5248👍, 0💬

How To Use LIKE Conditions
How To Use LIKE Conditions? - MySQL FAQs - Introduction to SQL Basics A LIKE condition is also called pattern patch. There are 3 main rules on using LIKE condition: '_' is used in the pattern to match any one character. '%' is used in the pattern to match any zero or more characters. ESCAPE clause i... 2007-05-11, 5111👍, 0💬

All rights in the contents of this web site are reserved by the individual author. fyicenter.com does not guarantee the truthfulness, accuracy, or reliability of any contents.