Question

我在sqlite

中的数据库中有3个表

表A


+-----+-------+
|  id | name  |
+-----+-------+
| 1   | Ann   |
| 2   | Bill  |
| 3   | Mike  |
| 4   | Zoey  |
+-----+-------+

表B

+-----+-----+
| idA | idC |
+-----+-----+
| 1   | 1   |
| 1   | 2   |
| 2   | 3   |
| 3   | 2   |
| 4   | 1   |
+-----+-----+

表C

+-----+-----+
|  id | type|
+-----+-----+
| 1   | x   |
| 2   | y   |
| 3   | z   |
+-----+-----+

我试过了：

CREATE VIEW test AS SELECT A.id, A.name, C.type
FROM A, B, C
WHERE B.idA = A.id
AND B.idB = B.id

然后我得到：


**View test**
+-----+-------+-------+
|  id | name  | type  |
+-----+-------+-------+
| 1   | Ann   | x     |
| 1   | Ann   | y     |
| 2   | Bill  | z     |
| 3   | Mike  | y     |
| 4   | Zoey  | x     |
+-----+-------+-------+

但是我想做这样的事情

+-----+-------+-------+
|  id | name  | type  |
+-----+-------+-------+
| 1   | Ann   | x,y   |
| 2   | Bill  | z     |
| 3   | Mike  | y     |
| 4   | Zoey  | x     |
+-----+-------+-------+

不重复任何一行，这是可能的吗？

Answer 1

SQLite支持GROUP_CONCAT()

CREATE VIEW test 
AS
SELECT  A.id, A.name, GROUP_CONCAT(C.type) AS Type
FROM    A, B, C
WHERE   B.idA = A.id AND 
        B.idC = C.id
GROUP   BY A.id, A.name

SQLFiddle Demo

输出

╔════╦══════╦══════╗
║ id ║ name ║ Type ║
╠════╬══════╬══════╣
║  1 ║ Ann  ║ x,y  ║
║  2 ║ Bill ║ z    ║
║  3 ║ Mike ║ y    ║
║  4 ║ Zoey ║ x    ║
╚════╩══════╩══════╝

来自SQLite文档

group_concat()函数返回一个字符串 X的所有非NULL值的串联。如果存在参数Y. 然后它被用作X实例之间的分隔符。逗号（“，”）如果省略Y，则用作分隔符。的顺序连接元素是任意的。

Answer 2

在定义视图时尝试使用此查询：

SELECT A.id, A.name, GROUP_CONCAT(C.type) type
FROM A
INNER JOIN B ON B.idA = A.id
INNER JOIN C ON C.id = B.idC
GROUP BY A.id

查看GROUP_CONCAT()

的MySQL文档

如何使用sqlite中的视图添加特定行中的列？

2 个答案: