Cumulative sum by date by products

[zxl1031]

I have found a couple of similar solved topics, but unfortunately I just cannot apply that into my modeling. Strange!

Can someone look into my case?

Table name: test.

The formula entered in the cum_sum column gives me the cumulative sum of values regardless of "product".

But I hope to get the cumulative sum of values as in "should_be_cum_sum" column. How to figure it out?

Thanks!