Optimizing query with multiple sums?

I have table products:

+----------+-----------+----------+---------+
|family_id |shopper_id |product_id|quantity |
+----------+-----------+----------+---------+
|A         |1          |Kit Kat   |10       |
|A         |1          |Kit Kat   |5        |
|A         |1          |Snickers  |9        |
|A         |2          |Kit Kat   |7        |
|B         |3          |Kit Kat   |2        |
+----------+---------- +----------+---------+

For each product, I want to calculate 2 totals:

• total quantity per shopper
• total quantity per family. Sum of total quantities for all shoppers in the same family.

The final table should look like:

+----------+----------+-------------------------+-----------------------+
|shopper_id|product_id|total_quantity_shopper   |total_quantity_family  |
+----------+----------+-------------------------+-----------------------+
|1         |Kit Kat   | 15                      | 22                    |
|1         |Snickers  | 9                       | 9                     |
|2         |Kit Kat   | 7                       | 22                    |
|3         |Kit Kat   | 2                       | 2                     |
+----------+----------+-------------------------|-----------------------|

This is my query:

SELECT
    distinct shopper_id,
    product_id,
    sum(quantity) OVER (PARTITION BY shopper_id, product_id) as total_quantity_shopper,
    sum(quantity) OVER (PARTITION BY family_id, product_id) as total_quantity_family
FROM
    products;

But looking at the query plan, it looks very inefficient (I think). How can I improve the query above?

I think the family is a hierarchy for the shopper. So, I would suggest group by and window functions:

select family_id, shopper_id, product_id,
       sum(quantity) as total_quantity_shopper,
       sum(sum(quantity)) over (partition by family_id, product_id) as total_quantity_family
from products
group by family_id, shopper_id, product_id