postgresql - GROUP BY 时前两个值的差异

Question

假设我有以下 SQL 表:

id | score
------------
1  |  4433
1  |  678
1  |  1230
1  |  414
5  |  8899
5  |  123
6  |  2345
6  |  567
6  |  2323

现在我想做一个GROUP BY id操作其中score列将修改如下:取每个 id 的前两个最高分之间的绝对差值.

例如，上述查询的响应应该是:

id  |  score
------------
1   |  3203
5   |  8776
6   |  22

如何在 PostgreSQL 中执行此查询？

Answer 1

使用 ROW_NUMBER 以及旋转逻辑，我们可以尝试:

WITH cte AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY id ORDER BY score DESC) rn
    FROM yourTable
)

SELECT id,
       ABS(MAX(score) FILTER (WHERE rn = 1) -
               MAX(score) FILTER (WHERE rn = 2)) AS score
FROM cte
GROUP BY id;

Demo