with t1 as (
    select job, count(score) as cnt
    from grade
    group by job
)
select job,
(case when MOD(cnt, 2) = 0 then round(cnt/2,0)
else CEILING(cnt/2) end) as start,
(case when MOD(cnt, 2) = 0 then round(cnt/2,0) + 1
else CEILING(cnt/2) end) as end
from t1
order by job;