What is the customer names of orders which have unit cost greater than 4000USD?
unit cost greater than 4000USD refers to Unit Cost > 4000;
SELECT T FROM ( SELECT DISTINCT CASE  WHEN T2.`Unit Cost` > 4000 THEN T1.`Customer Names` END AS T FROM Customers T1 INNER JOIN `Sales Orders` T2 ON T2._CustomerID = T1.CustomerID ) WHERE T IS NOT NULL