统计出各个title类型对应的员工薪水对应的平均工资avg。结果给出title以及平均工资avg，并且以avg升序排序

员工职称表和薪酬表通过员工号链接，用职称分类后以平均薪酬升序（默认）排列。

select t.title,avg(s.salary) as average
from titles as t
join salaries as s
on t.emp_no = s.emp_no
group by t.title
order by average