SELECT 
    tbo.DEPT_CODE
    ,tbd.DEPT_NAME
    ,tbo.ORDER_NO
    ,tbo.CUST_CODE
    ,tbc.CUST_NAME
    ,tbo.ORDER_AMT
FROM TBL_ORDERS tbo
INNER JOIN TBL_DEPT tbd
    ON tbo.DEPT_CODE = tbd.DEPT_CODE
LEFT OUTER JOIN TBL_CUST tbc
    ON tbo.CUST_CODE = tbc.CUST_CODE
ORDER BY
    tbo.DEPT_CODE, tbo.ORDER_NO;