Add query optimization scripts and results

sql/get_order_detail.sql

@@ -0,0 +1,15 @@
+-- query optimization - task 2
+-- changes:
+--   interpreted quantity as the number of items in an order, because I assumed that Little lemon wants
+--   orders à la carte instead of fixed menus
+
+prepare GetOrderDetail from "
+select
+    O.OrderID,
+    count(OI.MenuItemID) as Quantity,
+    O.BillAmount as Cost
+from Orders as O
+inner join OrderItems as OI on O.OrderID = OI.OrderID
+inner join Bookings as B on O.BookingID = B.BookingID
+where B.CustomerID = ?;
+";