select
    tor.DEPT_CODE AS DEPT_CODE,
    td.DEPT_NAME 
FROM
    TBL_ORDERS AS tor 
    left outer join TBL_DEPT AS td 
        on td.DEPT_CODE = tor.DEPT_CODE 
UNION 
select
    ts.DEPT_CODE AS DEPT_CODE,
    td.DEPT_NAME 
FROM
    TBL_SALES AS ts 
    left outer join TBL_DEPT AS td 
        on td.DEPT_CODE = ts.DEPT_CODE 
order by
    DEPT_CODE asc;