IFNULL() - MySQL Control Flow Function

The IFNULL() function in MySQL is used to return a specified value if the expression is NULL. This function comes under MySQL's control flow functions and is often used in data manipulation and reporting.

Syntax

IFNULL(expression, value)

Where:

• expression is the expression to be checked for NULL values
• value is the value to be returned if expression is NULL

Example

Suppose we have a table products with columns product_name, price, and discount. We want to calculate the final price of each product, taking the discount into account. However, some products do not have any discounts assigned yet, which should be treated as a 0 discount. Here's how we can use IFNULL() function to achieve this:

SELECT product_name, price, IFNULL(discount, 0) as discount, (price - IFNULL(discount, 0)) as final_price
FROM products;

In the query above, we use the IFNULL() function to replace any NULL values in the discount column with 0. Then, we calculate the final price by subtracting the (possibly) non-zero discount from the original price.

Output

When we run the above query in MySQL, we would see a table with columns product_name, price, discount, and final_price. The discount column would have any NULL values replaced with 0. The final_price would have the calculation performed and would show the result of subtracting the discount (if any) from the price.

Explanation

The IFNULL() function in MySQL is used to replace any NULL values with a specified value. This is useful when you want to make sure that your queries return correct results even if some values are missing. The function takes two arguments: the expression to be checked for NULL values and the value to be returned if the expression is NULL.

In the example above, we use the IFNULL() function to replace any NULL values in the discount column with 0 and then use the result in further calculations. If we did not use IFNULL() in our calculations, we could end up with erroneous results because NULL values would cause calculations that involve them to fail.

Use

IFNULL() function is frequently used in data manipulation, to handle missing or NULL values. It can be used in conjunction with other MySQL functions like CONCAT() or AVG(), to create custom calculations or consolidate missing values.

Important Points

• IFNULL() is a MySQL control flow function that returns a specified value if the expression is NULL.
• IFNULL() is often used in queries where a missing value or NULL can cause errors or erroneous results.
• You can also use the NULLIF() function to compare two expressions and return NULL if they are equal.

Summary

The IFNULL() function in MySQL is a powerful tool to handle NULL values in your queries. It can be used in various situations where handling or masking missing values is needed. By using the IFNULL()function in conjunction with other MySQL functions, you can create complex queries that provide accurate and consistent results.