按 ROW_NUMBER 排序

Question

UPD：谢谢大家，话题结束了，睡觉后我什么都明白了=）

我在理解 OVER 子句和 ROW_NUMBER 函数时遇到问题。简单表 - 名称和标记。我想计算每个名字的平均分。

SELECT top 1 with ties name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM table 
ORDER BY AVG(mark) OVER(PARTITION BY name)

它会显示类似这样的内容，我明白为什么 - 这就是 ROW_NUMBER() 所做的

name|number
Pete 1
Pete 2

但是如果我写

SELECT top 1 with ties name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM table 
ORDER BY AVG(mark) OVER(PARTITION BY name), number

它会显示

name|number
Pete 1

这一次我不明白 ORDER BY 如何与 ROW_NUMBER() 函数一起使用。谁能给我解释一下？

Answer 1

您当然可以按 ROW_NUMBER 列排序，因为 SELECT 子句在 ORDER BY 子句之前进行评估。您可以按任何列或列别名排序。这就是没有抛出错误消息的原因（因为它是有效的）。

SELECT name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM @table 
ORDER BY number

评估为

name       number
---------- --------------------
John       1
pete       1
pete       2
John       2
pete       3

OP 的第二个 row_number 示例不正确。

SELECT AVG(mark) OVER(PARTITION BY name), name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM @table 
ORDER BY AVG(mark) OVER(PARTITION BY name), number

按预期返回，因为 AVG 是第一个排序列，后跟数字。

            name       number
----------- ---------- --------------------
11          pete       1
11          pete       2
11          pete       3
17          John       1
17          John       2

将查询更改为 number DESC，pete 仍然是第一个，但是行号是降序的。

            name       number
----------- ---------- --------------------
11          pete       3
11          pete       2
11          pete       1
17          John       2
17          John       1

SQL 操作顺序

FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause

Answer 2

您不能直接按 ROW_NUMBER 排序：我不知道为什么您在这种情况下没有收到错误，但通常您会收到。因此使用派生表或 CTE

SELECT
    name, number
FROM
    (
    SELECT
       name,
       ROW_NUMBER() OVER (PARTITION BY name ORDER BY name) as number,
       AVG(mark) OVER (PARTITION BY name) AS nameavg
    FROM table
    ) foo
ORDER BY
   nameavg, number

但是，PARTITION BY name ORDER BY name 是没有意义的。每个分区都有随机顺序，因为排序是分区

我怀疑你想要这样的东西，其中 ROW_NUMBER 基于 AVG

SELECT
    name, number
FROM
    (
    SELECT
       name,
       ROW_NUMBER() OVER (PARTITION BY name ORDER BY nameavg) AS number
    FROM
        (
        SELECT
           name,
           AVG(mark) OVER (PARTITION BY name) AS nameavg
        FROM table
        ) foo
    ) bar
ORDER BY
    number

或者更传统的（但名称被折叠为平均值）

SELECT
    name, number
FROM
    (
    SELECT
       name,
       ROW_NUMBER() OVER (PARTITION BY name ORDER BY nameavg) AS number
    FROM
        (
        SELECT
           name,
           AVG(mark) AS nameavg
        FROM
           table
        GROUP BY
           name
        ) foo
    ) bar
ORDER BY
    number

您可以也许使用

将派生的 foo 和 bar 折叠成一个

ROW_NUMBER() OVER (PARTITION BY name ORDER BY AVG(mark))

但是 none 这是有道理的：我知道您的问题是关于 如何 它的工作原理的抽象问题，这个问题不清楚。如果您用简单的英语描述您想要的内容并带有示例输入和输出，那会更有意义