Add query optimization scripts and results

sql/cancel_order.sql

@@ -0,0 +1,9 @@
+-- query optimization - task 3
+-- noqa: disable=CP03
+create procedure CancelOrder (in TargetOrderID int)
+begin
+delete from Orders
+where OrderID = TargetOrderID;
+
+select concat("Order ", TargetOrderID, if(row_count() = 1, " is cancelled", " doesn't exist")) as Confirmation;
+end