When attempting to run this in the initial SQL does Tableau return any sort of error or warning? If so, could you include a screenshot possibly?
Also what is the underlying data source that is Tableau is attempting to connect to?(i.e. Oracle, SAP HANA, Microsoft SQL Server 2008?)
Is the Oracle connection published to Tableau Server? If so, check that the run as user has proper permissions to access the data source.
Otherwise, possibly submit a case to the Tableau Support team to have a deeper look into the issue. Support Case | Tableau Software