METHOD get_city_couples .
*check cityfrom is initial.
  SELECT DISTINCT cityfrom INTO TABLE cityfrom_tab FROM spfli.
  IF cityfrom IS NOT INITIAL.
    SELECT DISTINCT cityto INTO TABLE cityto_tab FROM spfli
    WHERE cityfrom = cityfrom.
  ELSE.
    SELECT DISTINCT cityto INTO TABLE cityto_tab FROM spfli.
  ENDIF.
ENDMETHOD.