Well… this has been a long discussion since 2019: what is the best choice/procedure to create an own shopping cart avoiding using so many rows during the process?
Using the normal/regular way (what Roldy mentioned and Glide uses in its Buy button) lets you to have an easy structure and know your inventory without complications but on the way to that happiness too many rows are used and sacrificed. It isn’t efficient and I hated that way always!
When the Joined List was created it helped too much and allowed to create another shopping cart style (easier and smarter) but we still have some problems and one of them is what you are having: the inventory and sale stats based on product.
Unfortunately a Set Column action currently doesn’t support a multiple relation yet otherwise, I think we would have a final solution for this issue.
Saludos amigo!