SELECT employee.*, department.*
FROM employee
LEFT JOIN department
ON employee.DepartmentID = department.DepartmentID
UNION ALL
SELECT employee.*, department.*
FROM department
LEFT JOIN employee
ON employee.DepartmentID = department.DepartmentID
WHERE employee.DepartmentID IS NULL
Following Jonathan Leffler's comment, here's an alternative answer to that of Mark Byers':
See here for original source and further SQLite examples.
Yes, see the example on Wikipedia.