Sorry for my English at first.

I’m learning SQL in W3schools’s SQL Tryit Editor. You may find there the same tables on which I operate.

How can I sum quantity of the same products?

I tried this:

SELECT Products.ProductName, OrderDetails.Quantity, Customers.Country
FROM Orders
JOIN OrderDetails ON Orders.OrderID = OrderDetails.OrderID
JOIN Products ON OrderDetails.ProductID = Products.ProductID
JOIN Customers ON Orders.CustomerID = Customers.CustomerID WHERE Customers.Country = 'Germany';

and it was my result:

SQL code and result

As you can see for example there is two rows with “Boston Crab Meat” and quantity of this didn’t sum.