select  a.LINE_ID as LINE,
        a.SEAT_NO as SEAT_F,
        a.SEAT_NO + 2 as SEAT_T
from 
(select
    LINE_ID,
    SEAT_NO,
    RSV_STATUS,
    row_number() over (partition by LINE_ID,RSV_STATUS order by LINE_ID desc) as 'フラグ連番',
    SEAT_NO  - row_number() over (partition by LINE_ID,RSV_STATUS order by LINE_ID desc) as 'NUM'
from
    SEAT_RESERVE
order by LINE_ID desc , SEAT_NO asc) as a
where a.RSV_STATUS = 0
    group by a.LINE_ID, a.NUM
    having count(a.NUM)   >= 3