1.分析
三个条件依次写出。

2.代码

select avg(salary) as avg_salary from salaries
where to_date = '9999-01-01'
and salary not in (select max(salary) from salaries where to_date = '9999-01-01')
and salary not in (select min(salary) from salaries where to_date = '9999-01-01')