SELECT S.DEPT_CODE, D.DEPT_NAME--DISTINCT O.DEPT_CODE, D.DEPT_NAME
FROM TBL_DEPT AS D
RIGHT JOIN TBL_SALES AS S ON D.DEPT_CODE=S.DEPT_CODE
UNION
SELECT O.DEPT_CODE, D.DEPT_NAME
FROM TBL_DEPT AS D
RIGHT JOIN TBL_ORDERS AS O ON D.DEPT_CODE=O.DEPT_CODE
ORDER BY O.DEPT_CODE;