题解 | 统计各个部门平均薪资

with t1 as (
    select department,(normal_salary - dock_salary) as salary
    from staff_tb join salary_tb using(staff_id)
)
select department,round(avg(salary),3) as avg_salary
from t1
where salary between 4000 and 30000
group by department
order by avg_salary desc;