with SEAT_3_VACANT as (
select
    LINE_ID
    ,SEAT_NO
    ,RSV_STATUS
    ,lag(RSV_STATUS) over (partition by LINE_ID 
        order by LINE_ID, SEAT_NO) as LAG_SEAT_ST
    ,lead(RSV_STATUS) over (partition by LINE_ID 
        order by LINE_ID, SEAT_NO) as LEAD_SEAT_ST
from
    SEAT_RESERVE
order by 1,2
)

select
    LINE_ID as LINE
    ,SEAT_NO - 1 as SEAT_F
    ,SEAT_NO + 1 as SEAT_T
from 
    SEAT_3_VACANT
where
    -- 勝手にNullは消える
    RSV_STATUS='0'
    and LAG_SEAT_ST='0'
    and LEAD_SEAT_ST='0'
order by 1 desc, 2