Filter one query with the results of another

Hi, I’m hoping to filter some data by using the results of another query. I found some documentation here Transform data | Grafana documentation but I don’t fully understand how it is done practically, there is a screenshot showing the end but I’m struggling to implement

I have two data sources

host | cpu | memory
A | 12.2 | 5.2
B | 15 | 3

host | project | department
A | X | Finance
B | Y | Finance

Got a variable in table 2 to filter by ‘Project’, so assuming I select X, I want to see A | 12.2 | 5.2 as my actual result

I have applied the transform filter data by query but it doesn’t appear to do anything, I sort of expecting I would have to tell it host was the key. Checking the debug of the transform the input just matches the output

Should this work? If so, what do I need to do to resolve it.