题解 | 统计各岗位员工平均工作时长

select post,round(avg(a.hours),3) as work_hours
from(
select staff_tb.staff_id,post,round(timestampdiff(second,first_clockin,last_clockin)/3600,3) as hours #直接用hour的话，会忽略分秒上的差异（因为提示里面举例了单个员工的工作时长，以h为单位，后面有三个小数点，说明员工分秒上面也是有数据的，算时间差时不能忽略）
from attendent_tb
left join staff_tb
on attendent_tb.staff_id=staff_tb.staff_id
having hours is not null) a
group by post
order by work_hours desc