Are you working with a Tableau Extract here? What is the second data source type?
I'm going to piggyback off of this question.
I'm trying to left join a SQL Server Extract to my SN ITSM Extract. I setup the SQL extract, add the SN ITSM connection/table, but as soon as I add the SN table I no longer have the option to add Extract filters. This makes my SQL Server "extract" try to pull in every single row which will not work for me.
How can I extract from SQL Server and join to SN extract?