You assume that all people have bosses. The top boss has no boss.
Isn't that why a left outer join is used?
Besides, if you are referring to question #1, a person without a boss can never be a part of the set of employees who have a higher salary than their boss.
Two assumptions to be clarified in the interview: 4th question above doesn't apply to the top boss (who can't have a greater salary than a boss he/she doesn't have, so no issue on the 1st question). Department table has an alternate key on department name.
Nitpicking, yes, but these questions certainly allow for a deeper discussion with the interviewer.