Question

我们假设有一个表'items'有三列：'id'，'pos'和'neg'，选择结果应按操作pos - neg的结果排序。< / p>

所以，以下应该有效：

SELECT
    id,
    pos - neg AS diff
FROM items
ORDER BY diff DESC

现在我需要获取特定行（在表格中）的位置，按“diff”排序结果。我试过这个：

WITH summary AS (
    SELECT
        i.id,
        i.pos - i.neg AS diff,
        ROW_NUMBER() OVER(ORDER BY diff) AS position
    FROM items i)
SELECT s.*  FROM summary s WHERE s.id = 351435254

但执行返回ERROR：列“diff”不存在。

那么，是否可以获得该位置，或者将差异保持在单独的列中会更好？

Answer 1

为避免重复计算，只需将ROW_NUMBER()移至外部查询...

WITH summary AS (
    SELECT
        i.id,
        i.pos - i.neg AS diff       
    FROM
        items i
)
SELECT
    s.*,
    ROW_NUMBER() OVER(ORDER BY s.diff) AS position
FROM
    summary s
WHERE
    s.id = 351435254

在内部查询期间，diff的引用范围仅限于 {/ 1}}之前存在的，否则您可以获得循环引用。

到外部查询时，您的新字段SELECT存在，因此可以作为参数提供给其他计算，函数等。

Answer 2

尝试：

WITH summary AS (
    SELECT
        i.id,
        i.pos - i.neg AS diff,
        ROW_NUMBER() OVER(ORDER BY (i.pos - i.neg)) AS position
    FROM items i)
SELECT s.*  FROM summary s WHERE s.id = 351435254

Postgres：如何在按操作结果排序时获取行号？

2 个答案: