SELECT 
  T1.DEPT_CODE
  ,T2.DEPT_NAME
FROM TBL_ORDERS T1
LEFT OUTER JOIN TBL_DEPT T2
ON T1.DEPT_CODE = T2.DEPT_CODE
UNION
SELECT
  T3.DEPT_CODE
  ,T4.DEPT_NAME
FROM TBL_SALES T3
LEFT OUTER JOIN TBL_DEPT T4
ON T3.DEPT_CODE = T4.DEPT_CODE;