finding an empty association

I have an interesting project where I need to find an agent_id from one table such that he has the least number of associated records (or preferably none) in a second table. Simple definition of the tables is: Agents Table: AgentID int primary key auto_increment FName, LName and other details of this agent Users Table: UserID int primary key auto_increment AgentID int --> AgentsTable Orders, Datestamp, other details The Agent is assigned to the User on a rotation basis, where an Agent who does not have any assignments, or has the least number is the next one to be picked. Is it possible to do a join of some kind (I'm not too good at joins) that would determine the Agent with the least number of associated records in the User table? Terry