Question

我有4个表：品牌，类别，brands_category和文件。品牌和类别由brands_category链接，brands_category有2列：brand_id和category_id

## brands ##
id  |  name |  url | ..

## category ##
id | name | order | ..

## brands_category ##
brand_id | category_id

## files ##
id | name | path | brand_id | uploaded_at

我希望从文件表中获取所有具有特定类别且按来自upload_at的不同品牌，而不重复品牌。我做了不少尝试，但无法得到我想要的结果。这是我取得的最大成功：

SELECT b.*, aa.uploaded_at
   FROM   brands b
   INNER JOIN
  (SELECT   bc.brand_id, f.uploaded_at
               FROM     brands_category bc
                        INNER JOIN brands b
                          ON b.id = bc.brand_id

                        INNER JOIN category c
                          ON c.id = bc.category_id
               INNER JOIN files f
               ON f.brand_id = bc.brand_id
               WHERE    c.id = 1
                GROUP BY bc.brand_id ORDER BY bc.brand_id DESC, f.uploaded_at DESC) aa
       ON b.id = aa.brand_id

我确实获得了类别为1的品牌，但是当品牌有多个与之关联的文件时，最新的uploaded_at日期不会返回。

Answer 1

不需要pivot表 - 只需使用标准joins：

select b.brand_id
from brands b
    join brands_category bc on b.brand_id = bc.brand_id
    join category c on bc.category_id = c.category_id
    join files f on b.brand_id = f.brand_id
where c.category_name = 'Some Category'
order by f.uploaded_at

A Visual Explanation of SQL Joins

使用连接和数据透视表选择mysql

1 个答案: