with ta as (
select * , sum(RSV_STATUS) over (PARTITION by LINE_ID order by SEAT_NO rows between 2 preceding and current row) as sum_res
from SEAT_RESERVE   
)

select LINE_ID as LINE, SEAT_NO - 2 as SEAT_F, SEAT_NO as SEAT_T
from ta
where SEAT_NO >= 3 and sum_res = 0
order by LINE desc, SEAT_NO asc