SELECT
SUB.LINE_ID AS LINE,
CASE
    WHEN SUB.THIRD = 0 THEN SUB.SEAT_NO - 2
END AS SEAT_F,
CASE
     WHEN SUB.THIRD = 0 THEN SUB.SEAT_NO
END AS SEAT_T
FROM
(
SELECT
*,
SUM(RSV_STATUS) OVER (PARTITION BY LINE_ID ORDER BY SEAT_NO ASC ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) AS THIRD
FROM
SEAT_RESERVE
) AS SUB
WHERE
SEAT_T IS NOT NULL AND (SEAT_T BETWEEN 3 AND 15) 
ORDER BY
LINE DESC,
SEAT_F ASC