SQL：加入多個不同大小的表格

Question

我不是一個在數據庫中工作很多的人，所以答案很簡單，但我無法找到它。 這裏是我的數據庫的簡化版本（這是在SQLITE BTW）：

我在我的數據庫中的以下值（我只把ID這裏，因爲只有它們是相關的）：

• device.id：1，2，3
• capability.id：10，20，30，40，50
• action.id：100，200，300，400，500
• action.id_capability ：10,30， 40，10，50

在這裏是在map_device_cap條目：

• 1,10
• 1,30
• 1,40
• 2,10
• 2， 20
• 2，50
• 3,20 20

條目中map_device_action：

• 1，100
• 1，200
• 1，300
• 2，400
• 2，500

現在我想要創建SELECT請求那個組表map_device_cap和map_device_action。在這種情況下，結果將是：

• 1，10，100
• 1，30，200
• 1,40 300
• 2，10，400
• 2,20，空
• 2，50，500
• 3，20，空

注意：表map_device_cap將始終大於map_device_action。

我第一次嘗試以下要求：

SELECT map_device_cap.id_device, map_device_cap.id_capability, 
     map_device_action.id_action 
FROM map_device_cap NATURAL LEFT JOIN map_device_action 

但這一要求給我的結果如下：

• 1，10，100
• 1，10，200
• 1，10，300
• 1，30，100
• 1，30，200
• 1，30，300
• 1,40 100
• 1,40 200
• 1,40 300
• 2，10，400
• 2，10，500
• 2,20，400
• 2,20，500
• 2，50，400
• 2，50，500
• 3，20，null

正如你所看到的那樣，有重複的條目，我不知道如何刪除它們。

如果有人有想法或需要更多信息，請告訴我。

問候

Answer 1

試試這個

SELECT mdc.id_device, 
     mdc.id_capability, 
     (SELECT (mda.id_action) 
     FROM action a 
     JOIN map_device_action mda 
       ON a.id_capability = mdc.id_capability 
       AND a.id = mda.id_action 
       AND mda.id_device = mdc.id_device 
     ) as a 
FROM map_device_cap mdc 
ORDER BY mdc.id_device, mdc.id_capability; 

Answer 2

一個辦法做到這一點是這樣的

SELECT c.id_device, 
     c.id_capability, 
     a.id 
FROM #map_device_cap c 
    JOIN #action a ON c.id_capability = a.id_capability 
    JOIN #map_device_action ma ON a.id = ma.id_action 
            AND c.id_device = ma.id_device 
UNION 
SELECT c.id_device, 
     c.id_capability, 
     NULL 
FROM #map_device_cap c 
    LEFT JOIN #map_device_action ma ON c.id_device = ma.id_device 
WHERE ma.id_device IS NULL; 

完整的腳本，我用我的測試：

IF OBJECT_ID('tempdb..#map_device_cap') IS NOT NULL 
    DROP TABLE #map_device_cap; 

CREATE TABLE #map_device_cap 
(id_device INT, 
id_capability  INT 
); 

INSERT INTO #map_device_cap 
VALUES 
(1, 
10 
); 

INSERT INTO #map_device_cap 
VALUES 
(1, 
30 
); 

INSERT INTO #map_device_cap 
VALUES 
(1, 
40 
); 
INSERT INTO #map_device_cap 
VALUES 
(2, 
10 
); 
INSERT INTO #map_device_cap 
VALUES 
(2, 
50 
); 
INSERT INTO #map_device_cap 
VALUES 
(3, 
20 
); 

select * from #map_device_cap 

IF OBJECT_ID('tempdb..#map_device_action') IS NOT NULL 
    DROP TABLE #map_device_action; 

CREATE TABLE #map_device_action(id_device INT, 
id_action  INT); 

INSERT INTO #map_device_action 
VALUES 
(1, 
100 
); 

INSERT INTO #map_device_action 
VALUES 
(1, 
200 
); 

INSERT INTO #map_device_action 
VALUES 
(1, 
300 
); 

INSERT INTO #map_device_action 
VALUES 
(2, 
400 
); 

INSERT INTO #map_device_action 
VALUES 
(2, 
500 
); 


select * from #map_device_action 


IF OBJECT_ID('tempdb..#action') IS NOT NULL 
    DROP TABLE #action; 

CREATE TABLE #action(id INT, 
id_capability  INT); 

INSERT INTO #action 
VALUES 
(100, 
10 
); 

INSERT INTO #action 
VALUES 
(200, 
30 
); 

INSERT INTO #action 
VALUES 
(300, 
40 
); 

INSERT INTO #action 
VALUES 
(400, 
10 
); 

INSERT INTO #action 
VALUES 
(500, 
50 
); 


SELECT c.id_device, 
     c.id_capability, 
     a.id 
FROM #map_device_cap c 
    JOIN #action a ON c.id_capability = a.id_capability 
    JOIN #map_device_action ma ON a.id = ma.id_action 
            AND c.id_device = ma.id_device 
UNION 
SELECT c.id_device, 
     c.id_capability, 
     NULL 
FROM #map_device_cap c 
    LEFT JOIN #map_device_action ma ON c.id_device = ma.id_device 
WHERE ma.id_device IS NULL; 

更新查詢，以滿足您的需求：

SELECT c.id_device, 
     c.id_capability, 
     a.id 
FROM map_device_cap c 
     JOIN action a ON c.id_capability = a.id_capability 
     JOIN map_device_action ma ON a.id = ma.id_action 
            AND c.id_device = ma.id_device 
UNION 
SELECT c.id_device, 
     c.id_capability, 
     NULL 
FROM map_device_cap c 
    LEFT JOIN map_device_action ma ON c.id_device = ma.id_device 
WHERE ma.id_device IS NULL 
UNION 
SELECT c.id_device, 
     c.id_capability, 
     NULL 
FROM map_device_cap c 
    LEFT JOIN action a ON c.id_capability = a.id_capability 
WHERE a.id_capability IS NULL;