with temp as 
(select job,
count(*) as num
from grade 
group by job)
select job,
round(case when num%2 = 1 then (num+1) / 2
when num%2 = 0 then num/2
end,0) as 'start',
round(case when num%2 = 1 then (num+1) / 2
when num%2 = 0 then (num/2)+1
end,0) as 'end'
from temp order by job;