ROW_NUMBER了分區，找到最大Rn值

Question

我從下表開始：使用查詢FO這個answer

+---+---------+----------+----------+-------------+----+ 
| 1 | OrderNO | PartCode | Quantity | DateEntered | rn | 
| 2 | 2144 | 44917 | 100  | 40773  | 1 | 
| 3 | 7235 | 11762 | 5  | 40773  | 1 | 
| 4 | 9999 | 60657 | 100  | 40773  | 1 | 
| 5 | 9999 | 60657 | 90  | 40774  | 2 | 
+---+---------+----------+----------+-------------+----+ 

：

+---+-----+---------+----------+----------+-------------+ 
| 1 | ID | OrderNO | PartCode | Quantity | DateEntered | 
| 2 | 417 | 2144 | 44917 | 100  | 40773  | 
| 3 | 418 | 7235 | 11762 | 5  | 40773  | 
| 4 | 419 | 9999 | 60657 | 100  | 40773  | 
| 5 | 420 | 9999 | 60657 | 90  | 40774  | 
+---+-----+---------+----------+----------+-------------+ 

了這一點。

select OrderNO,PartCode,Quantity,row_number() over(partition by OrderNO order by DateEntered desc) as rn 
from YourTable) as T 

現在，我想添加一個字段「rn_max」，shich是每個OrderNO的最大「RN」，並得到以下結果：

+---+---------+----------+----------+-------------+----+--------+ 
| 1 | OrderNO | PartCode | Quantity | DateEntered | rn | rn_max | 
| 2 | 2144 | 44917 | 100  | 40773  | 1 | 1  | 
| 3 | 7235 | 11762 | 5  | 40773  | 1 | 1  | 
| 4 | 9999 | 60657 | 100  | 40773  | 1 | 2  | 
| 5 | 9999 | 60657 | 90  | 40774  | 2 | 2  | 
+---+---------+----------+----------+-------------+----+--------+ 

我能得到這個結果計算每個訂單號的最大數量與查詢

SELECT OrderNO,MAX(rn) AS 'rn_max' 
FROM (
select OrderNO,PartCode,Quantity,row_number() over(partition by OrderNO order by DateEntered desc) as rn 
from YourTable 
) T 
Group by OrderNO 

然後使用來自YourTable的左連接。 是否有最短的方法來計算具有相同的OderNo的行？我試圖在查詢中添加row_number() over(partition by OrderNO) as rn_max，但我需要編寫一個order by子句。

Answer 1

使用max窗口功能。

SELECT T.*,MAX(rn) OVER(PARTITION BY OrderNo) AS 'rn_max' 
FROM (
select OrderNO,PartCode,Quantity,row_number() over(partition by OrderNO order by DateEntered desc) as rn 
from YourTable 
) T 

Answer 2

你可以試試這個。 基本上你會使用MAX（）聚集在分區的行，以獲得rn_max

select *, max(rn) over(partition by OrderNO) as rn_max 
FROM (
select OrderNO,PartCode,Quantity,row_number() over(partition by OrderNO order by DateEntered desc) as rn 
from YourTable 
) T