How to calculate two counts from 2 separate tables?

[Havana]

The left number represents the counts of total ad impressions from table A.
The right number represents the counts of total ad clicks from table B.
I want to create a new field named CTR(the left number / the right number)
and visualize it on the dashboard.
How can I do it?

[Alona_Nadler (AlonaN)]

Hey
You can do that using bucket script aggregation that is available in Visual Builder,
bucket script allows you to create your own customized formula and it can use existing aggregation
this is an example:

I had 2 aggregations, sum(quantity) and sum(review) and then using bucket script I divided them

Let me know if you have any questions
Alona

[Havana]

Thanks Alona.
I've come to this page which is in Visual Builder.
I want to count total impressions from table A and total clicks from table B.
So I should have 2 aggregations, one is count(created) from table A and another is count(created) from table B.
How to choose different tables in this interface?
Then I want to calculate click-through rate ( total_clicks/total_impressions)?