Searching for Nulls Using a SELECT Request
The IS NULL operator tests for the presence of nulls in a specified column. For example, to search for the names of all employees who have a null in the dept_no column, you could type the following request.
WHERE dept_no IS NULL;
This query produces the names of all employees having a null in the dept_no column. Because all employees contained in the employee table have been assigned to a department, no rows would be returned for this particular example.