Question

所以我有一些桌子。城市：

CI_ID | City
1     | Aberdeen
2     | Abingdon

国家：

CO_ID | Country
1     | United States of America
2     | Australia

省：

PR_ID | Province
1     | Alabama
2     | South Dakota

City_Province

CI_ID | PR_ID
1     | 2
2     | NULL

City_Country

CI_ID | CO_ID
1     | 1
2     | 2

通过创建视图我想拥有

CI_ID | City     | Province     | Country
1     | Aberdeen | South Dakota | United States of America
2     | Abingdon | NULL         | Australia

我无法弄清楚查询。

Answer 1

JOIN五个表格，但是LEFT JOIN Province表格如下：

创建视图：

CREATE VIEW AllData
AS
SELECT
  c.CI_ID, 
  c.city,
  p.Province,
  co.Country     
FROM City c
INNER JOIN City_Province cp ON c.CI_ID = cp.CI_ID
INNER JOIN City_Country cc ON cc.CI_ID = c.CI_ID
INNER JOIN Country co ON cc.CO_ID = co.CO_ID 
LEFT JOIN Province p ON p.PR_ID  = cp.PR_ID;

然后，只要您想从该视图中进行选择，就可以像普通表一样从中进行选择：

SELECT * FROM AllData

这会给你：

| CI_ID |     CITY |     PROVINCE |                  COUNTRY |
--------------------------------------------------------------
|     1 | Aberdeen | South Dakota | United States of America |
|     2 | Abingdon |       (null) |                Australia |

SQL Fiddle Demo

了解更多信息：

在单独的表上创建具有ip连接的三个表的视图

1 个答案:

SQL Fiddle Demo