MySQL in a Nutshell, 2nd Edition

Name

ISNULL()

Synopsis

ISNULL(column)

Use this function to determine whether the value of the argument given in parentheses is NULL. It returns 1 if the value is NULL and 0 if it is not NULL. Here is an example:

SELECT CONCAT(name_first, SPACE(1), name_last) AS Client,
telephone_work AS 'Work Telephone'
FROM clients
WHERE ISNULL(telephone_home);

In this example, after realizing that we don’t have home telephone numbers for several of our clients, we use the ISNULL() function in the WHERE clause of a SELECT statement to list client names and their work telephone numbers so that we can call them to get their home telephone numbers. Only rows in which the home_telephone column is NULL will result in a value of 1 and will therefore be shown in the results.