17.获取当前薪水第二多的员工的emp_no以及其对应的薪水salary

法一：row_number开窗函数(当薪水第二的人有多个时只会输出一个)

select emp_no,salary
from
(select emp_no,salary,row_number() over(order by salary desc) t
from salaries
where to_date='9999-01-01')
where t=2

法二：rank开窗函数(当薪水第二的人有多个时会全部输出)

select emp_no,salary
from
(select emp_no,salary,rank() over(order by salary desc) t
from salaries
where to_date='9999-01-01')
where t=2

法三：max()+子查询

select emp_no,max(salary)
from salaries
where salary <>(select max(salary)
from salaries
where to_date='9999-01-01')