Searching for Nulls and Nonnulls In the Same Search Condition
To search for nulls and non‑nulls within the same predicate, the search condition for nulls must be specified separately from any other search conditions.
For example, to select the names of all employees with the job title of ‘Vice Pres,’ ‘Manager,’ or null, you could type the following SELECT statement:
SELECT name, job_title
WHERE job_title IN (’Manager’ OR ’Vice Pres’)
OR job_title IS NULL;