mysql查询以连接其中一个表中没有关联的3个表

Question

SQLFIDDLE LINK

我有以下事件表。

活动

+---------+---------------+
| column  |     type      |
+---------+---------------+
| id      | int(11)       |
| title   | varchar(255)  |
| content | longtext      |
+---------+---------------+

event_attachment

+----------+---------------------------------+
|  column  |              type               |
+----------+---------------------------------+
| id       | int(11)                         |
| caption  | varchar(255)                    |
| type     | enum('AUDIO', 'VIDEO', 'IMAGE') |
| path     | varchar(255)                    |
| position | int(11)                         |
+----------+---------------------------------+

event_gallery

+---------------+---------+
|    column     |  type   |
+---------------+---------+
| event_id      | int(11) |
| attachment_id | int(11) |
+---------------+---------+

我可以从单独的查询中获取事件附件，例如 -

SELECT ea.id, ea.caption, ea.type, ea.path,  ea.position
FROM `event_attachment` ea
WHERE ea.id
    IN (SELECT eg.attachment_id FROM `event_gallery` eg WHERE eg.event_id = {$event_id})
ORDER BY ea.position ASC;

但我不能直接对event_attachment 和events 执行JOIN。

我也可以得到event，它是单个附件 -

SELECT e.title , eg.attachment_id
FROM `events` e 
JOIN `event_gallery` eg
    ON e.id = eg.event_id
GROUP BY e.id 

我无法让上述两个查询一起工作，并在单个查询中提供整个事件详细信息及其附件。

我想要的是在每个事件的第一个位置获取事件列表以及事件附件。现在，一个事件可能会或可能不会附加。

期望的输出 -

+----+-------------------+-------------------------------------------------------+------------------------------------------+----------+--+
| id |       title       |                        content                        |                   path                   | position |  |
+----+-------------------+-------------------------------------------------------+------------------------------------------+----------+--+
|  1 | Barclay Delacruz  | Soluta minim eiusmod laborum minima cumque fugiat     | e2d80cd9-7e4f-4a3d-92b5-d5c600367499.jpg |       1  |  |
|  2 | Lesley Strickland | Rem culpa dolor doloremque modi nisi esse exercita... | 2b15b00f-f094-469b-a56f-de7460326110.jpg |       1  |  |
+----+-------------------+-------------------------------------------------------+------------------------------------------+----------+--+

注意问题可能听起来重复，因为英语不是我的第一语言，而且很难将整个场景放在一个问题中。

Answer 1

这是基本的东西！

SELECT e.id event_id
     , e.title
     , CASE WHEN LENGTH(e.content) > 10 THEN CONCAT(TRIM(SUBSTR(e.content,1,7)),'...') ELSE e.content END content
     , ea.id attachment_id
     , CASE WHEN LENGTH(ea.caption) > 10 THEN CONCAT(TRIM(SUBSTR(ea.caption,1,7)),'...') ELSE ea.caption END caption
     , ea.type
     , CASE WHEN LENGTH(ea.path) > 10 THEN CONCAT(TRIM(SUBSTR(ea.path,1,7)),'...') ELSE ea.path END path
  FROM events e
  JOIN event_gallery eg
    ON eg.event_id = e.id
  JOIN event_attachment ea
    ON ea.id = eg.attachment_id
 WHERE ea.position = 1;

+----------+------------------+------------+---------------+------------+-------+------------+
| event_id | title            | content    | attachment_id | caption    | type  | path       |
+----------+------------------+------------+---------------+------------+-------+------------+
|        1 | Barclay Delacruz | Soluta...  |             1 | c          | IMAGE | e2d80cd... |
|        2 | Jeremy Ballard   | Sapient... |             4 | Ipsum q... | IMAGE | 2b15b00... |
+----------+------------------+------------+---------------+------------+-------+------------+

Answer 2

您可以为树表执行JOIN。类似的东西：

SELECT e.title, ea.attachment
FROM `event_attachment` ea
JOIN `event__gallery` ag 
ON ea.id = eg.attachment_id JOIN `event` e
ON eg.event_id = e.id
ORDER BY ea.position ASC;

如果这不是你想要的对不起，但我的英语最差，我理解这个问题。

编辑：

我已经在你的 SQLFIDDLE 中测试了我的查询，我认为这就是你想要的：

SELECT e.id, e.title, e.content, ea.path, ea.position
FROM `event_attachment` ea
JOIN `event_gallery` eg 
ON ea.id = eg.attachment_id JOIN `events` e
ON eg.event_id = e.id
GROUP BY e.id
ORDER BY ea.position ASC ;