SELECT 
    DISTINCT(SAL.DEPT_CODE) AS DEPT_CODE
    ,DEP.DEPT_NAME
FROM TBL_ORDERS AS ORD 
FULL OUTER JOIN TBL_SALES AS SAL 
    ON ORD.DEPT_CODE = SAL.DEPT_CODE
LEFT OUTER JOIN TBL_DEPT AS DEP
    ON ORD.DEPT_CODE = DEP.DEPT_CODE
ORDER BY DEPT_CODE;