mysql-选择多对多关系的另一面

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背景

我有三个表：(SQL小提琴：http://sqlfiddle.com/#!2/f7b33/11)

产品展示

+----+-----------+
| id |  product  |
+----+-----------+
|  1 | product_1 |
|  2 | product_2 |
|  3 | product_3 |
+----+-----------+

产品_功能

+------------+------------+
| product_id | feature_id |
+------------+------------+
|          1 |          1 |
|          1 |          2 |
|          1 |          3 |
|          1 |          4 |
|          2 |          1 |
|          2 |          3 |
|          3 |          4 |
+------------+------------+

特征

+----+-----------+
| id |  feature  |
+----+-----------+
|  1 | feature_1 |
|  2 | feature_2 |
|  3 | feature_3 |
|  4 | feature_4 |
+----+-----------+

然后,我选择像这样：

SELECT products.product,
       GROUP_CONCAT(features.feature) AS features
FROM   products
       LEFT JOIN products_features
              ON product_id = products.id
       LEFT JOIN features
              ON products_features.feature_id = features.id
GROUP  BY products.id

得到类似的东西：

+-----------+-----------------------------------------+
|  product  |                features                 |
+-----------+-----------------------------------------+
| product_1 | feature_1,feature_2,feature_3,feature_4 |
| product_2 | feature_1,feature_3                     |
| product_3 | feature_4                               |
+-----------+-----------------------------------------+

题

因此,一切都很棒,但是,我想做的就是只拥有具有feature_1和feature_3的东西,同时仍然获得其他功能.

换句话说,我想编写一个查询来获取我：

+-----------+-----------------------------------------+
|  product  |                features                 |
+-----------+-----------------------------------------+
| product_1 | feature_1,feature_2,feature_3,feature_4 |
| product_2 | feature_1,feature_3                     |
+-----------+-----------------------------------------+

我试过了：

SELECT products.product,
       GROUP_CONCAT(features.feature) AS features
FROM   products
       LEFT JOIN products_features
              ON product_id = products.id
       RIGHT JOIN features
              ON products_features.feature_id = features.id AND features.feature in ('feature_1','feature_3')

GROUP  BY products.id

但是我当然知道：

+-----------+---------------------+
|  product  |      features       |
+-----------+---------------------+
| (null)    | feature_4,feature_2 |
| product_1 | feature_1,feature_3 |
| product_2 | feature_3,feature_1 |
+-----------+---------------------+

因此,尽管我现在知道product_1和product_2是具有这些功能的产品,但是我看不到它们具有的其余功能.

什么查询将允许我指定feature_1和feature_3并得到以下响应？

+-----------+-----------------------------------------+
|  product  |                features                 |
+-----------+-----------------------------------------+
| product_1 | feature_1,feature_2,feature_3,feature_4 |
| product_2 | feature_1,feature_3                     |
+-----------+-----------------------------------------+

解决方法:

我认为最通用的方法是使用Have子句：

SELECT products.product,
       GROUP_CONCAT(features.feature) AS features
FROM   products
       LEFT JOIN products_features
              ON product_id = products.id
       LEFT JOIN features
              ON products_features.feature_id = features.id
GROUP  BY products.id
HAVING sum(features.feature = 'feature_1') > 0 and
       sum(features.feature = 'feature_3') > 0;

hading语句中的每个子句都在计算给定功能出现的次数.和要求两个功能都在最终结果集中.

编辑：

根据语句的结构,您还可以执行以下操作：

HAVING find_in_set('feature_1', features) > 0 and
       find_in_set('feature_3', features) > 0;

之所以可行,是因为您正在生成包含功能列表的列,并且使用逗号作为该列表的分隔符.

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