select tod.DEPT_CODE as DEPT_CODE, td.DEPT_NAME as DEPT_NAME
from TBL_ORDERS tod left outer join TBL_DEPT td on tod.DEPT_CODE = td.DEPT_CODE
union
select ts.DEPT_CODE as DEPT_CODE, td.DEPT_NAME as DEPT_NAME
from TBL_ORDERS ts left outer join TBL_DEPT td on ts.DEPT_CODE = td.DEPT_CODE;