Based on the wording of your question it sounds like you are trying to use a global data restriction. If you and and want to check against the logged in user's person record an exists or not exists statement like this might work well as your condition.
not exists ( select 1 from person where person.personid = :&PERSONID& and person.department= 'COMMERCIAL')
Checking against free text fields like I did in my example can by unreliable and cause lots of questions. My preference is checking to see if the logged in users is in a person group or security group. This still allows you to easily manage who can see the values but doesn't rely on a free text field.
Hope this helps, Phil