ABAP ALV显示问题

TYPES:BEGIN OF ty_header,
BELNR TYPE bseg-BELNR,
SAKNR TYPE BSEG-SAKNR,
NUM1(10) TYPE C,
NUM2(10) TYPE C,
zuonr TYPE bseg-zuonr,
VBELN TYPE vbak-VBELN,
POSNR1 LIKE vbap-posnr,
END OF ty_header.
DATA:BEGIN OF it_vbap OCCURS 0,
posnr like vbap-posnr,
END OF it_vbap.
FORM get_data.
select vbeln from vbak
into CORRESPONDING FIELDS OF TABLE it_header
where vbeln = '0000500010'.
LOOP AT it_header INTO wa_header.
SELECT posnr
from vbap
into CORRESPONDING FIELDS OF TABLE it_vbap
FOR ALL ENTRIES IN it_header
where vbeln = it_header-vbeln.
it_header-posnr1 = it_vbap-posnr .
MOVE-CORRESPONDING it_vbap to wa_header.
modify it_header FROM wa_header.
ENDLOOP.
ENDFORM.去VBAP里面多行的数据怎么写？不用INNER JOIN。