题解 | 平均工资

select
    avg(salary) as avg_salary
from 
    salaries
where 
    (to_date='9999-01-01' 
    and 
    salary<>(select max(salary) from salaries where to_date='9999-01-01'))
and
    (to_date='9999-01-01' 
    and 
    salary<>(select min(salary) from salaries where to_date='9999-01-01'))