SELECT
    dept.DEPT_CODE,
    DEPT_NAME,
    ORDER_NO,
    cust.CUST_CODE,
    CUST_NAME,
    ORDER_AMT

FROM
    TBL_ORDERS as orders
JOIN
    TBL_DEPT AS dept
    ON  orders.DEPT_CODE = dept.DEPT_CODE
LEFT JOIN
    TBL_CUST AS cust
    ON  orders.CUST_CODE = cust.CUST_CODE
ORDER BY
    dept.DEPT_CODE ASC, ORDER_NO ASC