SAP Business One query that retrieves purchase orders that have not been fully received yet, including those that have not been received at all or have been partially received

 SELECT 

    T0.DocNum AS 'PO Number',

    T0.DocDate AS 'PO Date',

    T1.ItemCode AS 'Item Code',

    T1.Dscription AS 'Item Description',

    T1.Quantity AS 'Quantity Ordered',

    ISNULL(T2.Quantity, 0) AS 'Quantity Received'

FROM 

    OPOR T0

    INNER JOIN POR1 T1 ON T0.DocEntry = T1.DocEntry

    LEFT JOIN (

        SELECT 

            BaseEntry, 

            BaseLine, 

            SUM(Quantity) AS Quantity 

        FROM 

            PDN1 

        GROUP BY 

            BaseEntry, 

            BaseLine

    ) T2 ON T1.DocEntry = T2.BaseEntry AND T1.LineNum = T2.BaseLine

WHERE 

    T0.DocStatus = 'O'

    AND (T2.Quantity IS NULL OR T1.Quantity > T2.Quantity)