MySQL IFNULL()

The MySQL IFNULL() function is used to handle NULL values in expressions or columns. It returns the first non-NULL expression from a list of expressions provided as arguments. If all expressions are NULL, it returns NULL.

The basic syntax of the IFNULL() function is as follows:

IFNULL(expression1, expression2)

Here’s how it works:

• expression1 is the expression that the function evaluates. If it is not NULL, the function returns expression1.
• expression2 is the fallback expression. If expression1 is NULL, the function returns expression2.

The IFNULL() function is especially useful for handling NULL values and providing default values when a column or expression is NULL.

Here are some examples to illustrate the use of the IFNULL() function:

1. Use the IFNULL() function to replace NULL values in the discount column with a default discount of 0:

   SELECT product_name, IFNULL(discount, 0) AS final_discount
   FROM products;

2. Use the IFNULL() function to return the first non-NULL value from a list of expressions:

   SELECT customer_name, IFNULL(phone_number, email, 'No contact information available') AS contact_info
   FROM customers;

3. Calculate the total price of an order, taking into account that the discount might be NULL:

   SELECT order_id, product_name, quantity, unit_price, IFNULL(discount, 0) AS applied_discount,
          quantity * unit_price * (1 - IFNULL(discount, 0)) AS total_price
   FROM order_details;

The IFNULL() function is a helpful tool for handling NULL values in SQL queries, allowing you to provide meaningful defaults or perform calculations while gracefully dealing with missing or undefined data.