with at as (
    select *,timestampdiff(second,first_clockin,last_clockin)/3600 as tmp
    from attendent_tb
)
select s.post,round(avg(tmp),3) as work_hours
from at join staff_tb s on at.staff_id=s.staff_id
group by s.post
order by work_hours desc

这题主要是timestampdiff(second,first_clockin,last_clockin)/3600 这一行。

如果单位不是second然后/3600，换算成小时。 而是直接用hour的话， 就会丢失精度， 比如相减是9.5小时，那么只会得到9小时。 离了大谱、