SQL-18、查找当前薪水排名第二多的员工编号emp_no

题解：

select e.emp_no emp_no, s.salary salary, e.last_name last_name, e.first_name first_name
from employees e inner join salaries s on e.emp_no = s.emp_no and s.to_date='9999-01-01'
where s.salary =
    (select max( s2.salary)
    from salaries s2
    where 
     s2.salary < 
         (select max(salary) from salaries where to_date='9999-01-01')
     and s2.to_date='9999-01-01');

思路：