php query error sqlite near where syntax error

hi i'm new in sqlite i'm trying to execute a query to sqlite database with php, but **near where syntax error ** occurs

here's the query:

"
  INSERT  INTO selectedObject ( museum , atwork , beaconCode , qrCode)
  VALUES ('".$museo."','" .$opera."','".$codiceBeacon."', '".$codice_qr_random."')
  WHERE NOT EXISTS(
                    SELECT museum , atwork
                    FROM selectedObject
                    WHERE museum = '".$museo."' AND atwork = '".$opera."'

                  )";

what's was wrong?