题解 | 统计加班员工占比

select department, 
concat(round(sum(case when timestampdiff(second, first_clockin, last_clockin)/60/60>9.5 then 1 else 0 end)/count(1)*100, 1), '%') ratio
from staff_tb a join attendent_tb b on a.staff_id=b.staff_id
group by department
order by ratio desc