题解 | 获取当前薪水第二多的员工的emp_no以及其对应的薪水salary

-- 自连接
select 
    e.emp_no,
    a.salary,
    e.last_name,
    e.first_name
from
    employees as e 
join 
    salaries as a using(emp_no)
join 
    salaries as a1
on  
    a.salary < a1.salary
where 
    date(a.to_date) = '9999-01-01'
    and 
    date(a1.to_date) = '9999-01-01'
group by 
    e.emp_no,
    a.salary,
    e.last_name,
    e.first_name
having 
    count(distinct a1.salary) = 1