I hope you got your problem solved by now. It sounds like you are (or at least, were) Data Blending.
The asterisks you saw are the ATTR aggregation function, meaning more than one value was present.
To get the behavior you want (a true Join), you are better off to blend your two sources upstream of Tableau.
What are / were the two data sources (e.g. Excel, mySQL, etc. ) ?