题解 | #查找排除当前最大、最小salary之后的员工的平均工资avg_salary#
select AVG(salary) avg_salary
from salaries
where salary not in (
select max(salary) from salaries where to_date = '9999-01-01'
union all # 不去除重复记录
select min(salary) from salaries where to_date = '9999-01-01'
)
and to_date = '9999-01-01' 
