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#

可以采用多表工作，即剔除最大值和最小值后的新表中计算avg：
select avg(s1.salary) as 'avg_salary'
from salaries s1
where salary not in (select MAX(salary) from salaries s2 where s2.to_date = '9999-01-01')
and s1.salary not in (select MIN(salary) from salaries s2 where s2.to_date = '9999-01-01')
and s1.to_date = '9999-01-01'
;