Thank you very much for your answer, I have found that option as well but the problem is that I need the Data Source Name in a calculated field because I want to use that as a basis of a relationship towards my secondary data source.
when you use a field from a secondary data source in a calculation , it automatically shows DATA SOURCE NAME.FIELD NAME
I'm trying to do what you said in order to identify my data source but I cannot. I tried to create a calculated field into the primary datasource, but didn't recognize the "data source name" you were talking.
The issue is the following: https://community.tableau.com/message/753597?et=watches.email.thread#753597
Do you know why?