Find and list the full name of customers who bought products above-average quantity.
full name of the customer = FirstName, MiddleInitial, LastName; above-average quantity = Quantity > AVG(Quantity);
SELECT T2.FirstName, T2.MiddleInitial, T2.LastName FROM Sales AS T1 INNER JOIN Customers AS T2 ON T1.CustomerID = T2.CustomerID GROUP BY T1.Quantity HAVING T1.Quantity > ( SELECT AVG(Quantity) FROM Sales )