PO with or Without Invoice Query in Oracle apps

/* Formatted on 6/8/2015 3:06:15 PM (QP5 v5.240.12305.39446) */

SELECT PO_DISTRIBUTION_ID, invoice_num

  FROM ap_invoice_distributions_all apid, ap_invoices_all api

 WHERE     api.invoice_id = apid.invoice_id

       AND apid.PO_DISTRIBUTION_ID IN (SELECT PO_DISTRIBUTION_ID

                                         FROM po_distributions_all

                                        WHERE PO_DISTRIBUTION_ID = '9598769')