select d.id, d.value, d.device
from (
    select
        id, value, device,
        count(*) over (partition by device) records_in_group,
        row_number() over (partition by device order by id) row_number
    from data
) d
inner join (
    select
        d.device,
        row_number() over (partition by d.device order by id) idx
    from data d
) n on n.device = d.device and row_number = floor(n.idx * records_in_group / 3)
order by d.device, d.id;