在sql 查询过程中经常有一种查询，某一类别的第一名 比如：

limingyao=# \d employee
                Table "public.employee"
   Column   |  Type   | Collation | Nullable | Default
------------+---------+-----------+----------+---------
 id         | integer |           |          |
 name       | text    |           |          |
 department | text    |           |          |
 salary     | integer |           |          |

查询 employee表每一个部门工资最高的员工信息

1. 第一种最直观的写法

SELECT  
    *
FROM
    employee
WHERE
    (department, salary) IN (
        SELECT 
            department,
            MAX(salary)
        FROM
            employee
        GROUP BY
            department
    )
ORDER BY
    department;

1. 使用窗口函数 row_number()

WITH ranked_employees AS (
    SELECT 
        ROW_NUMBER() OVER (
           PARTITION BY department ORDER BY salary DESC
        ) AS rn,
        *
    FROM 
        employee
)
SELECT
    *
FROM
    ranked_employees
WHERE
    rn = 1
ORDER BY 
    department;

1. 使用 distinct on

SELECT DISTINCT ON (department)
    *
FROM
    employee
ORDER BY
    department,
    salary DESC;

Note: 这三种写法结果是不相同?

https://stackoverflow.com/questions/3800551/select-first-row-in-each-group-by-group