SQL Server 2012查詢-來自同一表的外鍵

Question

我有一個名為RoleDetails的表，具有以下結構：

ROLE_ID - PK , 
NAME ,
PARENT_ROLE_ID FK ,
CREATED_BY_ID , 
MODIFIED_BY_ID

另一個表是user_details

USER_ID ,
USERNAME ,
FULLNAME

我如何查詢該表，以便在結果集中獲得RoleName，RoleId，ParentRoleId，ParentRoleName，CreatedByName和ModifiedByName。

到目前為止，我已經嘗試過：

SELECT 
    [ROLE_ID] AS ID, r.NAME AS [RoleName], 
    r.PARENT_ROLE_ID AS [ParentRoleID] , 
    (SELECT rd.NAME FROM dbo.ROLES rd 
     WHERE rd.ROLE_ID = r.PARENT_ROLE_ID ) AS [ParentRoleName], 
    CONCAT(ud.FIRST_NAME, ' ', ud.LAST_name) AS [CreatedByName] , 
    CONCAT(u.FIRST_NAME, ' ', u.LAST_name) AS [LastModifiedByName] 
FROM 
    dbo.ROLES r 
LEFT OUTER JOIN 
    user_details u ON r.MODIFIED_BY = u.USER_ID 
LEFT OUTER JOIN 
    dbo.USER_DETAILS ud ON r.CREATED_BY = ud.USER_ID 
WHERE 
    r.ROLE_ID = @iRoleID;

Answer 1

您將需要兩次連接user_detail表。 一次獲取創建用戶，一次獲取修改用戶。

SELECT    rd.Name, 
          rd.Role_ID, 
          rd.Parent_role_id,
          pr.Name, 
          ud.userName as CreatedByName, 
          udm.userName as ModifyByName
FROM RoleDetails as rd
INNER JOIN RoleDetails as pr
ON rd.Parent_Role_Id = pr.Role_id
INNER JOIN User_Detail as ud
on rd.Created_by_id = ud.user_id
INNER JOIN User_Detail as udm
ON rd.Modified_by_user = udm.user_id