SELECT ORDERS.DEPT_CODE AS DEPT_CODE, DEPT_NAME
FROM TBL_ORDERS AS ORDERS
LEFT JOIN TBL_DEPT AS DEPT
ON ORDERS.DEPT_CODE = DEPT.DEPT_CODE
UNION
SELECT SALES.DEPT_CODE AS DEPT_CODE, DEPT_NAME
FROM TBL_SALES AS SALES
LEFT JOIN TBL_DEPT AS DEPT
ON SALES.DEPT_CODE = DEPT.DEPT_CODE
ORDER BY DEPT_CODE