SQL分组依据为NULL

Question

我有一张桌子，像这样：

ID   ProductID   ProductName  Price
==   =========   ===========  =====
1    XX1           TShirt      10
2    XX1           TShirt      10
3    NULL          TShirt      10
4    XX2           Shirt       20
5    XX3           Shirt1      30

现在我希望以此为依据ProductName，结果将如下

ID   ProductID   ProductName  Price
==   =========   ===========  =====
1    XX1           TShirt      30
4    XX2           Shirt       20
5    XX3           Shirt1      30

谢谢

Answer 1

ProductID似乎与小组无关，所以不要使用它。要获取所有列，您可以使用CTE和排名函数，例如ROW_NUMBER：

WITH CTE AS(
   SELECT ID,   
          ProductID,   
          ProductName,  
          Price = SUM(Price) OVER (PARTITION BY ProductName),
          RN = ROW_NUMBER()  OVER (PARTITION BY ProductName ORDER BY ID)
   FROM dbo.TableName
)
SELECT CTE.* FROM CTE
WHERE RN = 1

如果要采用包含ProductID（不包含）的行，请NULL修改ORDER BY：

WITH CTE AS(
   SELECT ID,   
          ProductID,   
          ProductName,  
          Price = SUM(Price) OVER (PARTITION BY ProductName),
          RN = ROW_NUMBER()  OVER (PARTITION BY ProductName 
                                   ORDER BY CASE WHEN ProductID IS NOT NULL 
                                     THEN 0 ELSE 1 END, ID)
   FROM dbo.TableName
)
SELECT CTE.* FROM CTE
WHERE RN = 1