>> I would like the query to return 5 results; i.e., 4 distinct and one duplicate. <<
The easy way is a UNION, based on a guess about the DDL you did bother
to post and the uniquness of emp_id:
SELECT last_name, first_name
FROM Personnel
WHERE emp_id IN ('009', '008', '007', '006')
UNION
SELECT last_name, first_name
FROM Personnel
WHERE emp_id = '007'