从每个类别的多个表中选择最新的记录

Question

我有三个表* book_category，books和book_pictures *在我的mysql中。我想获得每本书类别的最新书籍订单通过修正。我使用这个查询来获取最新的书籍，它工作正常。

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，所以我得到book_pictures URL来显示图像的书。如何编写查询以从book_pictures表中获取最新书籍的URL？下面我告诉你表的结构。

 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

使用左加入，

我认为这会工作，也没有寿运行它。

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