select
    td.dept_code as DEPT_CODE
    , DEPT_NAME
    , ORDER_NO
    , tc.CUST_CODE as CUST_CODE
    , CUST_NAME
    , ORDER_AMT
from TBL_ORDERS tos
inner join TBL_DEPT td on tos.dept_code=td.dept_code
left join TBL_CUST tc on tos.cust_code=tc.cust_code
order by 1, 3;