select job, (case when max(r)%2=1 then round((max(r)+1)/2,0) else round(max(r)/2,0) end) start, (case when max(r)%2=1 then round((max(r)+1)/2,0) else round(max(r)/2+1,0) end) endd
from
(select *, row_number()over(partition by job order by score) r
from grade) t1
group by job