#子查询方法
select emp_no,salary from salaries
where salary = (select distinct salary 
from salaries 
order by salary desc 
limit 1,1)
order by emp_no ;

#dense_rank()窗口函数
select emp_no,salary from 
(select emp_no,salary,dense_rank()over(order by salary desc) r
from salaries) t
where t.r=2