What is the average number of customers per sales person?
average = DIVIDE(COUNT(CustomerID), COUNT(EmployeeID));
SELECT CAST(COUNT(T1.CustomerID) AS REAL) / COUNT(T3.EmployeeID) FROM Customers AS T1 INNER JOIN Sales AS T2 ON T1.CustomerID = T2.CustomerID INNER JOIN Employees AS T3 ON T2.SalesPersonID = T3.EmployeeID