SELECT
    D.DEPT_CODE,
    D.DEPT_NAME,
    O.ORDER_NO,
    C.CUST_CODE,
    C.CUST_NAME,
    O.ORDER_AMT
FROM
    TBL_ORDERS O 
    INNER JOIN TBL_DEPT D 
        ON  O.DEPT_CODE = D.DEPT_CODE
    LEFT OUTER JOIN TBL_CUST C
        ON O.CUST_CODE = C.CUST_CODE
ORDER BY
    D.DEPT_CODE ASC,
    O.ORDER_NO ASC;