Write the SQL code that will list Physician-Person appointments only ONCE. : This one is confusing me? 

This is what I have so far : 

<code>SELECT DISTINCT Appointment_date_time FROM Appointment 
INNER JOIN Person ON 
Appointment.Person_ID = Person.Person_ID
INNER JOIN Physician ON 
Physician.Physician_ID = Person.Physician_ID
HAVING COUNT(*) < 1</code>