题解 | 统计各个部门平均薪资
select
department,
avg(normal_salary - dock_salary) as avg_salary
from
staff_tb st,
salary_tb sa
where
st.staff_id = sa.staff_id
and normal_salary - dock_salary <= 30000
and normal_salary - dock_salary >= 4000
group by
department
order by
avg_salary desc