SQL JOIN和第二個表中的一些條件的限制結果

Question

我有兩個表。

投資組合：

+----+-------+--------------+ 
| 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 | 
+----+------------+--------------+--------------+-----------------+ 

我怎樣才能查詢得到結果如下圖所示：

結果：

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

我想要做的是加入投資組合表照片表，並照片表的一些條件限制的結果：

1. user_id是不是空
2. created_at是「第二古老」。

「第二最老的」 含義是，例如，我有4個日期時間： 2017/08/11，2017/08/12，2017/08/16，2017/08/19。

在這種情況下，「第二最老」是2017/08/12。

我已經嘗試過自己：

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; 

，並用Google搜索這一點，但發現沒有解決我的問題。

任何幫助？ 感謝您的進步！

Answer 1

我已經使用了兩個GROUP BY構造。我省略了Portfolios表，因爲它似乎並不重要

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

Answer 2

像拉迪姆，我不明白，需要加入到投資組合，因爲這無助。我的解決方案使用ROW_NUMBER（）函數：

SELECT port_id, port_name, id as photo_id, created_at as photo_created_at FROM 
(select *, row_number() OVER (PARTITION BY port_id ORDER By created_at) AS rn from 
photos WHERE user_id IS NOT NULL) r 
WHERE r.rn = 2 

然而，就感鏈接到投資組合如果照片不重複port_name中指！理論上講，port_name不應該在照片中！

編輯

如果您從照片port_name中指那麼你需要：

SELECT r.port_id, p.port_name, r.id as photo_id, r.created_at as photo_created_at FROM 
(select *, row_number() OVER (PARTITION BY port_id ORDER By created_at) AS rn from 
photos WHERE user_id IS NOT NULL) r INNER JOIN portfolios p on p.id = r.port_id 
WHERE r.rn = 2