I believe that the two data tables that are held within the Oracle database can be joined in the connection process with a state written in the 'Initial SQL' statement. Then this can be blended or joined within Tableau, based on a common field in the two data sources. I am attaching a few different product helps for this use case that would most be beneficial in developing a solution.
The following link talks about utilizing the initial SQL within the connection window for the Oracle connection. Run Initial SQL
Additionally I am attaching a knowledge base article that touches on the use of custom joins in several different scenarios: Defining Custom Joins with the Custom SQL Option | Tableau Software
Oracle Data Source | Product Help
I hope this helps get you started with resolving the issue.