表数据：

image.png

实现结果（对薪水进行排名）：

image.png

sql语句实现

1.子查询只能返回一条数据，如果子查询返回多条数据则会出错。
2.每一条select子查询只能查询一个字段。

SELECT
  s1.emp_no,
  s1.salary,
  (SELECT
    COUNT(DISTINCT s2.salary)
  FROM
    salaries s2
  WHERE s2.to_date = '9999-01-01'
    AND s2.salary >= s1.salary) AS `rank`  -- 去重：计算并列排名
FROM
  salaries s1
WHERE s1.to_date = '9999-01-01'
ORDER BY s1.salary DESC,
  s1.emp_no ;

窗口函数实现
SELECT
  emp_no,
  salary,
  dense_rank () over (
ORDER BY salary DESC) AS `rank`
FROM
  salaries
WHERE to_date = '9999-01-01' ;