The best way is using View insted of computing OrderValue, because you should update this field every time when Quantity
or Price
are changed. This is not good and it contradicts 3NF also you will have a lot of other promlems. I strongly recommend to you change database structure, but if you would not change you can use following example:
insert into Orders(OrderId, OrderDate, OrderValue)
values(@SomeOrderID,getdate(), 0)
insert into Products(ProductId, ProductName, Price)
values(/*some values*/)
insert into OrderDetails(DetailsId, OrderId, ProductId, Quantity)
values(/*some values, include @SomeOrderID*/)
update o set OrderValue = (p.Price* pd.Quantity)
from Orders o
inner join OrderDetails pd on pd.OrderId = o.OrderId
inner join Products p on p.ProductId = pd.ProductId
where o.OrderId= @SomeOrderID