Using fields for select conditions

FORM f_ext_tdata USING fld_slct fld_from fld_whre
                       fld_entr TYPE STANDARD TABLE
                 CHANGING it_into TYPE STANDARD TABLE.
  IF fld_entr[] IS INITIAL.
    SELECT (fld_slct)
      FROM (fld_from)
      INTO TABLE @it_into
      WHERE (fld_whre).
  ELSE.
    SELECT (fld_slct)
      FROM (fld_from)
      INTO TABLE @it_into
      FOR ALL ENTRIES IN @fld_entr
      WHERE (fld_whre).
  ENDIF.
ENDFORM.

PERFORM f_ext_tdata
    USING
      'bukrs, butxt'
      't001'
      'bukrs EQ @lt_bseg-bukrs'
      lt_bseg[]
    CHANGING
      lt_t001[].