從每個類別的多個表中選擇最新記錄

Question

我的mysql中有三個表* book_category，books和book_pictures * 。 我想通過修改來獲取每個書籍類別順序的最新書籍。 我使用此查詢來獲取最新書籍，並且效果很好。

select * from (select * from books ORDER BY amended DESC) AS x GROUP BY book_sub_category_id

但我想加入我的book_pictures表，以便獲取book_pictures網址以顯示圖書圖像。 如何編寫查詢以從book_pictures表中獲取帶有URL的最新書籍？ 下面，我向您展示表格的結構。

       book_category
+-------------+-----------------+
|category_id  | category_name   |
|-------------------------------|             
|    ca       |   custom Act    |
|    ct       |   Custom Tarif  |
|-------------+-----------------+

                          books
+-------------+-----------------+-----------------+--------------------------+
|    book_id  |   category_id   |   name          |        amended           |
|-------------------------------|-----------------+--------------------------|             
|    01       |      ca         | custom Act      |      01-06-2011          |
|    02       |      ca         | custom Act      |      01-06-2012          |
|    03       |      ca         | custom Act      |      01-06-2013          |
|    04       |      ct         | custom tarif    |      01-07-2011          |
|    05       |      ct         | custom tarif    |      01-07-2012          |
|    06       |      ct         | custom tarif    |      01-07-2013          |
+-------------+-----------------+-----------------+--------------------------+   

                               book_pictures
+-------------+-----------------+-----------------+--------------------------+
| picture_id  |   book_id       |   small_url     |        large_url         |
|-------------------------------|-----------------+--------------------------|             
|    p1       |      01         |      url        |      url                 |
|    p2       |      02         |      url        |      url                 |
|    p3       |      03         |      url        |      url                 |
|    p4       |      04         |      url        |      url                 |
|    p5       |      05         |      url        |      url                 |
|    p6       |      06         |      url        |      url                 |
+-------------+-----------------+-----------------+--------------------------+

Answer 1

使用左聯接，

我認為這會奏效，還沒有運行。

SELECT * FROM (
                SELECT b.*, 
                       p.large_url 
                FROM     books b 
                    LEFT JOIN book_pictures p 
                        ON b.book_id = p.book_id 
                ORDER BY b.amended DESC 
               ) AS x 
GROUP BY book_sub_category_id