Viewing of the underlying data is data source specific. Have you investigated if the data sources involved support a cross-database join? i ask because this would allow you to create a single data source for both data sources.
What version of Tableau are you using as well?
Can you try cross join if your secondary data source allows that. That way cross join will result in single table and viewing the data wont be issue any more.
Since I am using tableau 9.3 where crossdatabse join is not possible, so can you please provide a solution where I can join both the table without the help of data blending.