Initialize sql with session variable
Sometimes we connect the data with the view(VL) with the user environment variable and it will return blank row .It's because when we connect with the database.We didn't assign the environment variable. So we should alter environment session when we connect the session
ALTER SESSION SET nls_language='AMERICAN';
https://kb.tableau.com/articles/issue/no-data-returned-from-an-oracle-view-when-using-nls-language