I am doing analysis for the quantity of product purchased. I have few table to join to get other details from the table. As you can see from the sql fiddle, i am trying to sum the quantity of product received, and if quantity received is null then will get the value of ordered quantity. The output show is incorrect since it only shows me the id cart = 1. By right i want it to show both cart id 1 and 2 and sum of quantity of product id..