Answer: Using SAVEPOINT

START TRANSACTION;
-- Step 1: Capture baseline values
SELECT Quantity, Stock INTO @orig_qty, @orig_stock
FROM   Order_Details od 
JOIN   Products p ON od.ProductID = p.ProductID
WHERE  od.OrderID = 3 AND od.ProductID = 3;
-- Step 2: Apply the first update to increase quantity and decrease stock, then create a savepoint
UPDATE Order_Details
SET    Quantity = Quantity + 2
WHERE  OrderID = 3 AND ProductID = 3;
UPDATE Products
SET    Stock = Stock - 2
WHERE  ProductID = 3;
SAVEPOINT sp_first_update;
-- Step 3: Perform another update to simulate a second change
UPDATE Order_Details
SET    Quantity = Quantity + 1
WHERE  OrderID = 3 AND ProductID = 3;
UPDATE Products
SET    Stock = Stock - 1
WHERE  ProductID = 3;
-- Step 4: Roll back to the savepoint to undo only the latest change while keeping the first
ROLLBACK TO SAVEPOINT sp_first_update;
-- Step 5: Query the data to display all stages of the transaction
SELECT 'Before Changes' AS Stage, @orig_qty AS OrderLineQuantity, @orig_stock AS ProductStock
UNION ALL
SELECT 'After First Update', Quantity, Stock 
FROM   Order_Details od JOIN Products p ON od.ProductID = p.ProductID
WHERE  od.OrderID = 3 AND od.ProductID = 3
UNION ALL
SELECT 'After ROLLBACK TO SAVEPOINT', @orig_qty, @orig_stock;
-- Step 6: Roll back the transaction to leave the database unchanged
ROLLBACK;