Excluding Nulls From Query Results
The IS NOT NULL operator excludes rows having a null in a specified column from the results of a query.
For example, to search for the names of all employees with non‑nulls in the job_title column, you could type the following request.
WHERE job_title IS NOT NULL;
The result of this query is the names of all employees with a non‑null in the job_title column. For this particular example, the names of all employees are returned because every employee has, by definition, been assigned a job title.