Using query variable

Hello, I am very new to Grafana.

I would like to build boom table with query like

sum(sellercenter_income_total) by (seller))

But this gives me lots of data and I can’t save a dashboard.

For this reason I tried to limit the data

topk(20, sort_desc(sum(sellercenter_income_total) by (seller)))

but it sorts data incorrectly.

I found that I can create query variable in order to get correct sorting.

I created a query variable with query

query_result(topk(20, sort_desc(sum(sellercenter_income_total) by (seller))))

The problem is that I don’t know how to use this variable in boom table.
Using just $variable_name doesn’t work for me.

Can you please help me to figure it out?

Thank you.