Check if invoice already exists

Hi,

I want to check if an invoice is already in the system before I can create it with an own dynpro (with reduced fields). The criteria should be vendor, comp_code, ref_doc_no_long. I still need to add the total sum.

Currently I am using the following code (but this will only identify the parked invoices):

select b~belnr into (lv_inv_no) from bkpf as b

   inner join vbsegk as v

    on  v~belnr = b~belnr

    and v~bukrs = b~bukrs

   where

   v~lifnr = lv_vendor_no

   and b~bukrs = ls_documentheader-comp_code

   and b~xblnr eq ls_documentheader-ref_doc_no_long

   and b~blart in ('KD', 'NE')

   .

endselect.

Can someone make a suggestion which tables I need to check for the posted documents and the logistic (parked) invoices?

Is it correct to check also the XREVERSAL field and select only those that are empty (and not 1 or 2)?

Regards,

  Vanessa