problem while data retrieving

Hi,

I am unable to retrieve exnum1.

SELECT SINGLE docyr exnum INTO (itab-docyr,itab-exnum) FROM j_1iexchdr WHERE rdoc = itab-vbeln.
  IF itab-docyr IS NOT INITIAL AND itab-exnum IS NOT INITIAL.
SELECT SINGLE exnum INTO itab-exnum1 FROM  j_1iexcdtl WHERE trntyp = 'ARE1' AND docyr = itab-docyr AND werks = itab-werks AND
     rdoc2 = itab-exnum.

ENDIF.
MODIFY itab TRANSPORTING docyr exnum exnum1.

Regards

Kalpana