有條件的SQL從幾個表中連接

Question

我有三個連接的表。我需要做一個單一的SQL選擇，我知道我需要使用某種形式的連接，但不是如何。我只希望如果用戶ID的會話訪問該object's區（用戶獲得訪問權限，如果他們的公司進入該地區的）我的表格要選擇的是的objectID：

+----------+--------+ Objects 
| objectID | areaID | 
+----------+--------+ 
|  1 |  2 | 
|  2 |  2 | 
|  3 |  3 | 
+----------+--------+ 
+-----------+--------+ Users 
| companyID | userID | 
+-----------+--------+ 
|   1 |  1 | 
|   1 |  2 | 
|   1 |  3 | 
+-----------+--------+ 
+-----------+--------+ Access 
| companyID | areaID | 
+-----------+--------+ 
|   1 |  1 | 
|   1 |  2 | 
|   1 |  3 | 
+-----------+--------+ 

Answer 1

選擇用戶名和使用companyID在inner query中對應的區域ID。然後使用從對象表使用內通過inner query

形成表再次加入此，選擇不同的ObjectID嘗試此查詢： -

Select distinct a.objectID 
from 
Objects a 
inner join 
(
Select a.*,b.areaID 
from 
Users a 
inner join 
Access b 
on a.companyID=b.companyID 
) b 
on a.areaID=b.areaID 
Where b.UserID= 1; 

Answer 2

如果我理解你的權利，這似乎就像兩個INNER JOIN功能會得到結果你要找的：

WITH ONE AS (
    SELECT a.companyID, a.userID, b.areaID 
    FROM Users a 
    INNER JOIN Access b 
    ON a.companyID = b.companyID 
    ) 

SELECT a.companyID, a.userID, a.areaID, b.objectID 
FROM ONE a 
INNER JOIN Objects b 
ON a.areaID = b.areaID; 

編輯：回覆評論

如果你想限制結果爲特定用戶ID值，你需要一個WHERE條款：

WITH ONE AS (
    SELECT a.companyID, a.userID, b.areaID 
    FROM Users a 
    INNER JOIN Access b 
    ON a.companyID = b.companyID 
    ) 

SELECT a.companyID, a.userID, a.areaID, b.objectID 
FROM ONE a 
INNER JOIN Objects b 
ON a.areaID = b.areaID 
WHERE a.userID = ${specific_user_id};