Inconsistent Weekday Values Returned from Oracle Custom SQL in Tableau

Steps to Reproduce

1. Create an Oracle table with a DATE column.

2. Insert sample dates (for example, from 19-Nov-2025 to 28-Nov-2025) and commit the data.

3. Run a Custom SQL query using:

SELECT
  date_column,
  TO_CHAR(date_column, 'D') AS weekday_num
FROM table_name;

4. With NLS_TERRITORY = 'AMERICA', observe weekday values such as:

Sunday = 7

Monday = 1

Tuesday = 2

5. Change the Oracle session setting:

ALTER SESSION SET NLS_TERRITORY = 'SWITZERLAND';

6. Re-run the same query and observe different weekday values for the same dates (for example, Sunday = 6, Monday = 7, Tuesday = 1).

7. Create a Tableau workbook using this Custom SQL and verify that weekday-based logic reflects these differences.