Write SQL query to solve given problem: Calculate the total quantity of purchased product that has been prepared by employee number 257 and is in pending shipment status.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(T2.OrderQty) FROM PurchaseOrderHeader AS T1 INNER JOIN PurchaseOrderDetail AS T2 ON T1.PurchaseOrderID = T2.PurchaseOrderID WHERE T1.Status = 1