我可以從子查詢中獲得逗號分隔的值嗎？如果沒有，如何做到這一點？

Question

我有一個表

Create table Country_State_Mapping 
(
    Country nvarchar(max), 
    State nvarchar(max) 
) 

隨着5個記錄。

Insert into Country_State_Mapping values('INDIA', 'Maharastra') 
Insert into Country_State_Mapping values('INDIA', 'Bengal') 
Insert into Country_State_Mapping values('INDIA', 'Karnatak') 
Insert into Country_State_Mapping values('USA', 'Alaska') 
Insert into Country_State_Mapping values('USA', 'California') 

我需要寫一個SQL查詢，它會給我2記錄/ 2列如下。

第一柱Contry和第二AllStates

1結果（2列）將是

印度和馬哈拉施特拉，孟加拉，卡納塔克

第二

美國和阿拉斯加California

我試過我喜歡這

select distinct 
    OutTable.Country, 
    (select State 
    from Country_State_Mapping InnerTable 
    where InnerTable.Country = OutTable.Country) 
from Country_State_Mapping AS OutTable 

，但沒有奏效...

Answer 1

SELECT Country, AllStates = 
    STUFF((SELECT ', ' + State 
      FROM Country_State_Mapping b 
      WHERE b.Country = a.Country 
      FOR XML PATH('')), 1, 2, '') 
FROM Country_State_Mapping a 
GROUP BY Country 

Answer 2

這是一個有點討厭的和潛在的緩慢，如果在Country_State_Mapping表中的記錄數量很大，但它確實把工作做好。它使用公用表表達式的遞歸功能在SQL 2005年推出

;WITH Base 
AS 
(
    SELECT 
     ROW_NUMBER() OVER (PARTITION BY Country ORDER BY Country, [State] DESC) AS CountryRowId, 
     ROW_NUMBER() OVER (ORDER BY Country, [State]) AS RowId, 
     Country, 
     [State] 
    FROM Country_State_Mapping 
), 
Recur 
AS 
(
    SELECT 
     CountryRowId, 
     RowId, 
     Country, 
     [State] 
    FROM Base 
    WHERE RowId = 1 

    UNION ALL 

    SELECT 
     B.CountryRowId, 
     B.RowId, 
     B.Country, 
     CASE WHEN R.Country <> B.Country THEN B.[State] ELSE R.[State] + ',' + B.[State] END 
    FROM Recur R 
    INNER JOIN Base B 
     ON R.RowId + 1 = B.RowId 
) 

SELECT * 
FROM Recur 
WHERE CountryRowId = 1 
OPTION (MAXRECURSION 0)--Dangerous