How to Use the MySQL NULLIFF() Function
In this tutorial, you will learn how to use the MySQL NULLIF() function, which compares two expressions and returns NULL if equal; otherwise returns the first expression.
MySQL NULLIF() Syntax
The syntax of the NULLIF() function is as follow:
NULLIF (expression_1, expression_2)
The following statement compares two integers and returns as Message:
SELECT NULLIF (1, 2) AS Message;
Since integer 1 is not equal to 2, the NUlLIF() function returns 1, the first expression.
The following statement returns NULL because both expressions of the NULLIF() function are equal:
SELECT NULLIF ("Apple", "Apple") AS Message;
The following statement returns NULL because both expressions are equal:
SELECT NULLIF ("The tutorial of NULLIF function.", "THE TUTORIAL of NULLIF Function.") AS Message;
As you can see, both expressions are not the same if you consider that lowercase and uppercase are different; NULLIF() is not case-sensitive, so lowercase and uppercase are treated the same.
Here is an example of using the SUM() function in the NULLIF():
SELECT NULLIF(SUM(1+2), 2) AS Message;
This statement returns 3. The integer 3 is the return value of SUM(1+2), which is greater than 2.
In this tutorial, you have learned how to use the MySQL NULLIF function. NULLIF() returns a null value if both expressions are equal; otherwise, it returns the first expression.