Selection, with validation of the fields

DATA: ls_where(72) TYPE c,

lt_where LIKE TABLE OF ls_where,

* create where condition
  IF NOT stru_node_vbak-vbeln EQ ''.
    CONCATENATE 'VBELN = ''' stru_node_vbak-vbeln '''' INTO ls_where.
    APPEND ls_where TO lt_where.
  ENDIF.


IF NOT stru_node_vbak-erdat EQ '00000000'.
    CONCATENATE 'ERDAT = ''' stru_node_vbak-erdat '''' INTO ls_where.
    IF stru_node_vbak-vbeln NE ''.
      CONCATENATE 'AND' ls_where INTO ls_where SEPARATED BY space.
    ENDIF.
    APPEND ls_where TO lt_where.
ENDIF.

SELECT VBELN ERDAT ERZET ERNAM ANGDT BNDDT AUDAT VBTYP TRVOG AUART
         AUGRU GWLDT SUBMI LIFSK FAKSK NETWR WAERK VKORG VTWEG SPART
         VKGRP VKBUR GSBER GSKST GUEBG GUEEN KNUMV
  FROM vbak INTO TABLE lt_vbak WHERE (lt_where).