SQL JOIN 并限制第二个表中某些条件的结果

Question

我有两个表。

投资组合:

+----+-------+--------------+
| id | name  | created_date |
+----+-------+--------------+
| 1  | Port 1| 2017/08/12   |
+----+-------+--------------+
| 2  | Port 2| 2017/08/14   |
+----+-------+--------------+
| 3  | Port 3| 2017/08/15   |
+----+-------+--------------+

照片:

+----+------------+--------------+--------------+-----------------+
| id | Port_name  | port_id 　　　| user_id 　　　| created_at      |
+----+------------+--------------+--------------+-----------------+
| 1  | Port 1     |          1   |       null   |    2017/08/10   |
+----+------------+--------------+--------------+-----------------+
| 2  | Port 2     |          2   |       null   |    2017/08/11   | 
+----+------------+--------------+--------------+-----------------+
| 3  | Port 3     |          3   |       null   |    2017/08/12   |
+----+------------+--------------+--------------+-----------------+
| 4  | Port 1     |          1   |          1   |    2017/08/13   | 
+----+------------+--------------+--------------+-----------------+
| 5  | Port 2     |          2   |          1   |    2017/08/14   |
+----+------------+--------------+--------------+-----------------+
| 6  | Port 3     |          3   |          1   |    2017/08/15   | 
+----+------------+--------------+--------------+-----------------+
| 7  | Port 2     |          2   |          1   |    2017/08/16   |
+----+------------+--------------+--------------+-----------------+
| 8  | Port 3     |          3   |          1   |    2017/08/17   |
+----+------------+--------------+--------------+-----------------+
| 9  | Port 2     |          2   |          1   |    2017/08/18   |
+----+------------+--------------+--------------+-----------------+
|10  | Port 3     |          3   |          1   |    2017/08/19   |
+----+------------+--------------+--------------+-----------------+

如何查询得到如下结果:

结果:

+---------+------------+----------------+-----------------+
| Port_id | port_name  | photo_id       | photo_created_at|
+---------+------------+----------------+-----------------+
| 2       | Port 2     |       7        |    2017/08/16   | 
+---------+------------+----------------+-----------------+
| 3       | Port 3     |       8        |    2017/08/17   |
+---------+------------+----------------+-----------------+

我想做的是加入 Portfolios 表和 Photos 表，并在某些条件下限制 Photos 表的结果:

1. user_id 不为空
2. created_at 是“第二老”。

“第二老”的意思是，例如，我有 4 个日期时间: 2017/08/11, 2017/08/12, 2017/08/16, 2017/08/19 >。

在这种情况下，“第二老”是 2017/08/12。

我自己试过:

SELECT p.id as Port_id, 
       p.name as Port_name, 
       ph.id as photo_id, 
       ph.created_at as photo_created_at 
FROM "Portfolios" AS p
LEFT JOIN (
          SELECT * 
          FROM "Photos" 
          WHERE user_id IS NOT NULL 
          ORDER BY created_at ASC 
          LIMIT 1 OFFSET 1) as ph
ON p.id = ph.port_id;

并用谷歌搜索，但没有找到解决我的问题的方法。

有什么帮助吗？ 提前致谢!

Answer 1

我使用了两个 GROUP BY 结构。我省略了 Portfolios 表，因为它似乎并不重要

select photos.port_id, min(photos.id), min(photos.created_at)
from photos
join 
(
  select port_id, min(created_at) photos_ca_min
  from photos
  where user_id is not null
  group by port_id
) p on p.port_id = photos.port_id
where photos.created_at > p.photos_ca_min and user_id is not null
group by photos.port_id

SQLFiddle