po line items to grpo

Question

I have 2 condtions in my query if my line item from po (container no) having a grpo so it should display 'shipment received' if no grpo so it should display 'no shipment received' need your expertise here please.

SELECT
    OPOR.DocNum ,
    POR1.U_ContainerNo ,
    CASE
        WHEN POR1.U_ContainerNo IS NOT NULL THEN 'Shipment Received'
        ELSE 'No Shipment Received'
    END 
FROM
    OPOR
INNER JOIN POR1 ON POR1.DocEntry = OPOR.DocEntry 
LEFT JOIN
    OPDN ON OPOR.DocEntry = OPDN.DocEntry
LEFT JOIN
    PDN1 ON POR1.DocEntry = PDN1.BaseEntry