题解 | 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

#   1.请你统计出各个title类型【group by】对应的员工薪水对应的平均工资avg【avg()】。
#   2.结果给出title以及平均工资avg，
#   3.并且以avg升序排序
#   思路：表连接+聚合+排序+注意当前筛选
select t.title, avg(s.salary)
from titles t join salaries s on t.emp_no = s.emp_no
where t.to_date = '9999-01-01' and s.to_date = '9999-01-01'
group by t.title
order by avg(salary)

/*如果表里的字段为唯一字段，可以不用在该字段前面加具体所属表名。考虑到可读性，最好是加上
select title, avg(salary)
from titles t join salaries s on t.emp_no = s.emp_no
where t.to_date = '9999-01-01' and s.to_date = '9999-01-01'
group by title
order by avg(salary)
*/