获取SQL Server中每个组中的顶级ID

Question

我想添加一个包含每个组中第一个列的列。

样品：

Product       ID
Orange        1
Orange        2
Orange        3
Orange        4
Apple         5
Apple         6
Apple         7
Grapes        8
Grapes        9

期望的输出：

Product       ID
Orange        1
Orange        1
Orange        1
Orange        1
Apple         5
Apple         5
Apple         5
Grapes        8
Grapes        8

Answer 1

您可以使用MIN(ID) OVER (PARTITION BY Product)：

SELECT Product, 
       ID = MIN(ID) OVER (PARTITION BY Product)
FROM dbo.Products
ORDER BY ID

Demo

今天的文章：Understanding the OVER clause

Answer 2

我觉得蒂姆正确！ 其他情况，你可以使用： SELECT P.Product FROM dbo.Products P CROSS APPLY (SELECT TOP 1 ID FROM dbo.Products WHERE Product = P.Product ORDER BY ID)