题解 | #获取所有员工当前的manager#
统计出当前各个title类型对应的员工当前薪水对应的平均工资
http://www.nowcoder.com/practice/c8652e9e5a354b879e2a244200f1eaae
select t.title,avg(sa.salary)
from salaries sa right join titles t
on sa.emp_no = t.emp_no
where t.title is not NULL
group by t.title
order by avg(sa.salary);
用右连接时可以这样写，若不加where 会报title为空的错误；也可以直接用左连或内联，不用加where
