轉換多個恢復從連接到一個逗號分隔的列表

Question

我有這個疑問：

SELECT 
    c.FirstName + ' ' + c.LastName AS Name, 
    r.Name AS Roles 
FROM 
    Contacts c 
    JOIN AspNetUsers u on c.ContactID = u.ContactID 
    JOIN AspNetUserRoles ur on u.id = ur.UserId 
    JOIN AspNetRoles r on ur.RoleId = r.Id 

返回一組是這樣的：

Name  Roles 
----------------------- 
Bob Jones Admin 
Bob Jones Agent 
Jane Smith Broker 
Jane Smith Buyer 

我想是這樣的：

Name  Roles 
----------------------- 
Bob Jones Admin, Agent 
Jane Smith Broker, Buyer 

我一直在玩COALESCE和GroupBy，但我似乎無法得到正確的組合。

Answer 1

另一種方法是將在CTE原始查詢，然後創建了最後的總結

;with cte as (
    SELECT 
     c.FirstName + ' ' + c.LastName AS Name, 
     r.Name AS Roles 
    FROM 
     Contacts c 
     JOIN AspNetUsers u on c.ContactID = u.ContactID 
     JOIN AspNetUserRoles ur on u.id = ur.UserId 
     JOIN AspNetRoles r on ur.RoleId = r.Id 
) 
Select A.Name 
     ,Roles = Stuff((Select Distinct ', ' +Roles From cte Where Name=A.Name For XML Path ('')),1,2,'') 
From (Select Distinct Name from cte) A 

Answer 2

您可以使用XML字符串執行此操作，就像您可以看到Google是「SQL Server string aggregate」一樣。

在你的情況下，查詢可能不明顯，因爲JOIN s。我覺得這是最好的辦法：

SELECT c.FirstName + ' ' + c.LastName AS Name, 
     STUFF((SELECT ',' + r.Name 
       FROM AspNetUsers u JOIN 
        AspNetUserRoles ur 
        ON u.id = ur.UserId JOIN 
        AspNetRoles r 
        ON ur.RoleId = r.Id 
       WHERE c.ContactID = u.ContactID 
       FOR XML PATH (''), TYPE 
      ).VALUE('.', 'nvarchar(max)' 
        ), 1, 1, '') 
      as Roles 
FROM Contacts c; 

這裏的關鍵是，你不想做聚集在外部查詢，如果你能避免它。相反，它使用相關的子查詢。

注意：這不是正好等於，因爲它會返回沒有角色的用戶。