Oracle PLS-00049: bad bind variable - oracle

Question

I'm getting this error when I try to create this trigger. I tried everything but I don't know what seems to be the problem.
Here is the code:
CREATE OR REPLACE TRIGGER after_price_update
AFTER UPDATE
ON Item
FOR EACH ROW
DECLARE new_totalprice INT;
BEGIN
IF :OLD.price <> :new.price THEN
new_totalprice := :old.Quantity * :new.price;
INSERT INTO OrderRecord(OrderRecord_Id, Item_Id, Employee_Id, Reservation_Id, Order_Time, Quantity, TotalPrice)
VALUES(old.OrderRecord_Id, old.Item_Id, old.Employee_Id, old.Reservation_Id, old.Order_Time, old.Quantity, new_totalprice);
END IF;
END;
And the error is:
4/22 PLS-00049: bad bind variable 'OLD.QUANTITY'
The tables look like this:
CREATE TABLE Item (
Item_Id int PRIMARY KEY,
Menu_Id int,
Name varchar2(20),
Description varchar2(120),
Price int,
FOREIGN KEY(Menu_Id) REFERENCES Menu(Menu_Id)
);
CREATE TABLE OrderRecord (
OrderRecord_Id int PRIMARY KEY,
Item_Id int,
Employee_Id int,
Reservation_Id int,
Order_Time date,
Quantity int,
TotalPrice int,
FOREIGN KEY(Item_Id)References Item(Item_Id),
FOREIGN KEY(Employee_Id)References Employee(Employee_Id),
FOREIGN KEY(Reservation_Id)References Reservation(Reservation_Id)
);

Answer 1

Table OrderRecord is not the table being updated: you cannot reference an old value for this table; you need to read this value with some SELECT statement.
IF :OLD.price <> :new.price THEN
new_totalprice := <Quantity> * :new.price;

Answer 2

There is no column Quantity in the table ITEM on which you are applying trigger.

Answer 3

If I understand what you are wanting to do correctly, it looks like you want to update the calculated total price of all existing OrderRecord entries when an Item entry has a price change.
CREATE OR REPLACE TRIGGER after_price_update
AFTER UPDATE
ON Item
FOR EACH ROW
BEGIN
IF NVL(:OLD.Price, 0) <> NVL(:new.Price, 0) THEN
-- Update the child table "OrderRecord" for this item using new price
UPDATE OrderRecord SET TotalPrice = Quantity * :new.Price WHERE Item_Id = :new.Item_id;
END IF;
END;
Note that this trigger is on the parent table, Item, and references two values from the modified record: price and Item_Id, to update the child OrderRecord table.
Also note the use of NVL to watch for nulls because the comparison will not succeed if a null is on either side. Using zero for null is debatable; one could use a value that will never occur such as a negative number.