Question

我有4个表：团队，用户，用户团队和权限：

用户：

UserID | Name
------------------------
1      | John
2      | Mike
3      | Tom

队：

TeamID | Name
-------------------------------
1      | FC Barcelona
2      | Real Madrid
3      | Manchester United
4      | Liverpool

权限：

PermissionsID | Name
-------------------------------
1             | Read Comments
2             | Write Comments
3             | Send Email
4             | Admin

UserTeams：

ID | UserID | TeamID | PermissionID
--------------------------------------------
1  | 1      | 1      | 1
2  | 1      | 1      | 2
3  | 1      | 1      | 4
4  | 1      | 2      | 1
4  | 1      | 4      | 3

-

UserID = 1（我们在查询之前知道这一点）

我想让查询得到这样的结果：

Permission.Name | FC Barcelona | Real Madrid | Manchester United | Liverpool | etc...
----------------------------------------------------------------------------
Read Comments   | (something)  | (something) | NULL              | NULL
Write Comments  | (something)  | NULL        | NULL              | NULL
Send Email      | NULL         | NULL        | NULL              | (something)
Admin           | (something)  | NULL        | NULL              | NULL

团队数量不限。

有什么想法吗？如果有多个查询，我不介意......

提前致谢！

的解的

首先选择团队：

SELECT TeamID, name FROM Teams

然后使用团队数据创建一个新查询：

SELECT     
Permissions.name as 'permissionName', 

<Loop this line with the previous query>
    MAX(CASE WHEN Teams.name = 'FC Barcelona' THEN Teams.name ELSE NULL END) AS 'FC Barcelona'
<End loop>

FROM Permissions
LEFT JOIN UserTeams ON UserTeams.PermissionID = Permissions.PermissionID AND UserTeams.UserID = '1' 
LEFT JOIN Teams ON Teams.TeamID = UserTeams.TeamID   
GROUP BY Permissions.name

现在我们得到了我们想要的结果。

Answer 1

我认为你的表格不完整......将会存储“（某物）”

Answer 2

查询结果中的列数不可变，您将始终获得相同数量的列。所以我建议像这样的查询结果：

Permission     | Team                |  User_name |  User_id
-----------------------------------------------------------------
Read Comments  | FC Barcelona        | John       | 1
Write Comments | Real Madrid         | John       | 1
Send Email     | Manchester United   | Mike       | 2
Admin          | ...(unlimited)      | Tom        | 2

（当然有正确的值;））

对此的SQL查询是：

SELECT 
    p.Name AS Permission,
    u.Name AS User_name,
    t.Name AS Team,
    u.id AS User_id
FROM
    UserTeams AS ut
INNER JOIN
    Users AS u ON (ut.UserId = u.UserId)
INNER JOIN
    Teams AS t ON (ut.TeamId = t.TeamId)
INNER JOIN
    Permissions AS p ON (ut.PermissionId = p.PermissionsId)
WHERE
    u.UserID = :userId

具有多个表的复杂MySQL查询（有关详细信息，请参阅）

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2 个答案: