All fields must be aggregate or constant when using multiple data sources tableau

Hello!

I have 2 extracts and want to create calculation field using data from both.

1st type: I download extracts from Tableau Server on my PC and connect them to Desktop with relashionshipThen I create a calculation field like this: SUM(IF [item_id]=[item_id (Extract1)] AND [platform]=[platform (Extract1)] AND

[date] = [reg_date] THEN [rev_7] END)/SUM([cost]) and it works fine.

2nd type: I connect to this extracts on Tableau Server from Desktop and use blend of them, I think (red chain near some fields in one of sources). Then I just create identical calculation field and it doesn't work. I even try this formula: IF ATTR([item_id])=ATTR([Extract1].[item_id]) AND ATTR([platform])=ATTR([Extract1].[platform]) AND

ATTR([date]) = ATTR([Extract1].[reg_date]) THEN SUM([Extract1].[rev_7]) END/SUM([cost]) and it doesn't work also.

Thank you in advance.

Andrew