REPORT  ZSTUDY
DATA: begin of BOOK occurs 0,
      carrid like sbook-carrid,
      connid like sbook-connid,
      end of book.
DATA: begin of FLIGHT occurs 0,
      carrid like sflight-carrid,
      connid like sflight-connid,
      end of FLIGHT.

SELECT carrid connid FROM SBOOK into corresponding fields of table BOOK
    WHERE SBOOK~CARRID eq 'AA' and
                SBOOK~CONNID eq '17'.

IF not BOOK IS INITIAL.
  SELECT carrid connid into corresponding fields of table FLIGHT
  FROM SFLIGHT
  FOR ALL ENTRIES IN BOOK
  WHERE SFLIGHT~CARRID eq BOOK-CARRID.
ENDIF.
            WRITE: / FLIGHT-carrid.

IF not BOOK[] IS INITIAL.
...
ENDIF.
LOOP AT FLIGHT.
  WRITE: / FLIGHT-carrid.
ENDLOOP.