Question

我需要在两个表中选择外键相互匹配，但我不想重复相同的外键。

我在数据库上有这些表：

    |Photo| (0/*) --------- (1)|Advertisement|

    |Photo|
       -photo_id
       -url
       -advertisement_id

    |Advertisement|
       -advertisement_id
       ...

数据库数据

    |Photo|
       photo_id | url | advertisement_id
           1    |  x  |        1
           2    |  x  |        1
           3    |  x  |        2
           4    |  x  |        3

我想要这个：

       ID   | URL  
       1    |  x
       2    |  x    -> It is anyone url   
       3    |  x

我在下面尝试SQL，但这个重复ID =（

    SELECT a.advertisement_id as ID, p.url as URL  
    FROM Advertisement a  
    RIGHT JOIN Photo p
    ON a.advertisement_id = p.advertisement_id
    LIMIT 6

结果：

    ID  |  URL  
    1   |   http://i0.statig.com.br/bancodeimagens/18/46/2h/18...
    2   |   http://www.yaves.es/images/Animales/Tiernos-Gatito...
    2   |   http://images.forwallpaper.com/files/thumbs/previe...
    10  |   http://www.petmag.com.br/img/gatos/racas/7892/euro...
    7   |   http://www.gmstatic.com/content/images/1369932859_...
    8   |   http://www.navegandonaweb.com/wp-content/uploads/2...

有人帮我构造sql查询吗？

Answer 1

SELECT a.advertisement_id as ID, p.url as URL  
FROM Advertisement a  
RIGHT JOIN Photo p
ON a.advertisement_id = p.advertisement_id
GROUP BY a.advertisement_id
ORDER BY p.photo_id ASC (or DESC ? )
LIMIT 6

OR

SELECT a.advertisement_id as ID, p.url as URL  
FROM Advertisement a,Photo p
WHERE a.advertisement_id = p.advertisement_id
GROUP BY a.advertisement_id
ORDER BY p.photo_id ASC (or DESC ? )
LIMIT 6

SQL SELECT不同的外键

1 个答案: