MySQL ISNULL() Function

 The ISNULL() function in MySQL is used to check whether an expression is NULL. It returns a boolean value: 1 if the expression is NULL, and 0 if it is not.

Syntax:

ISNULL(expression)

• expression: The value or column that you want to check for NULL.

Example 1: Check if a column value is NULL

SELECT ISNULL(column_name) AS is_null
FROM table_name;

This query checks if the column_name contains NULL values and returns 1 for rows where the value is NULL and 0 for rows where it is not.

Example 2: Using ISNULL() in a WHERE clause

SELECT *
FROM employees
WHERE ISNULL(email);

This will return all rows where the email column is NULL.

Example 3: Using ISNULL() with a specific value

SELECT ISNULL(NULL) AS result;

This will return 1 because the value is NULL.

In MySQL, the ISNULL() function is sometimes confused with the IFNULL() function. The key difference is:

• ISNULL() checks whether the value is NULL (returns 1 or 0).
• IFNULL() is used to replace a NULL value with a specified value.