按顺序取最后一个值

Question

我正在尝试将数据从源 table 插入目标 table，在目标 table 中，我有一个名为 SaleTo[= 的附加列31=].

SaleTo = 基于 MAX SaleSequence 的 SaleFrom。

来源示例table：

SaleNo	SaleFrom	SaleSequence
1	Alabama	2
1	Minnesota	1
1	Virginia	3

目标示例 table：

SaleNo	SaleFrom	SaleSequence	SaleTo
1	Alabama	2	Virginia
1	Minnesota	1	Virginia
1	Virginia	3	Virginia

我试过的一些代码：

SELECT DISTINCT a.SaleNo, 
                MAX(a.SaleSequence ) AS SaleSequence,
                b.SaleFrom
FROM SequenceOrderSource a
INNER JOIN SequenceOrderSource b
ON a.SaleNo= b.SaleNo
--WHERE B.SaleFrom IN (SELECT b.SaleFrom FROM SequenceOrderSource HAVING SaleSequence= MAX(SaleSequence))
GROUP BY a.SaleNo, b.SaleFrom

非常感谢任何帮助。

Answer 1

您可以使用last_value。默认范围是 RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW 因此您需要明确指定子句。

SELECT SaleNo, SaleSequence, SaleFrom,
   last_value(SaleFrom) over(partition by SaleNo order by SaleSequence RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) SaleTo
FROM SequenceOrderSource;

Answer 2

在这种情况下，另一种方法是使用 CROSS APPLY。像这样的代码：

SELECT SaleNo, SaleSequence, SaleFrom, OrderData.SaleFrom AS SaleTo
   CROSS APPLY (SELECT TOP 1 SaleFrom FROM SequenceOrderSource 
                ORDER BY SaleSequence DESC) OrderData
FROM SequenceOrderSource;