MySQL從多對多關係中選擇父行

Question

我有三個表，products,ingredients和ingredient_product。

我需要找到所有的products，其中產品有相關的成分。 它還需要在percentage列上具有匹配值。

產品存在與兩個相關的成分。

+-----+------------+---------------+------------+ 
| id | product_id | ingredient_id | percentage | 
+-----+------------+---------------+------------+ 
| 1 |   1 |   1 |   50 | 
| 2 |   1 |   2 |   50 | 
+------------------+--------------+-------------+ 

SQL檢索：

SELECT 
     products.id 
    FROM 
     products, 
     ingredient_product 
    WHERE 
     ingredient_product.product_id = products.id 
    AND 
     (ingredient_product.ingredient_id = 1 AND ingredient_product.percentage = 50) 
    AND 
     (ingredient_product.ingredient_id = 2 AND ingredient_product.percentage = 50) 

但這返回一個空的結果。 Empty set (0.00 sec)

產品：

+-------------------+-----------------------+------+-----+---------+----------------+ 
| Field    | Type     | Null | Key | Default | Extra   | 
+-------------------+-----------------------+------+-----+---------+----------------+ 
| id    | int(10) unsigned  | NO | PRI | NULL | auto_increment | 
| name    | varchar(255)   | NO |  | NULL |    | 
| short_description | text     | YES |  | NULL |    | 
| long_description | text     | YES |  | NULL |    | 
+-------------------+-----------------------+------+-----+---------+----------------+ 

主料：

+-------------------+-----------------------+------+-----+---------+----------------+ 
| Field    | Type     | Null | Key | Default | Extra   | 
+-------------------+-----------------------+------+-----+---------+----------------+ 
| id    | int(10) unsigned  | NO | PRI | NULL | auto_increment | 
| short_name  | varchar(50)   | NO |  | NULL |    | 
| thumbnail   | varchar(255)   | NO |  | NULL |    | 
+-------------------+-----------------------+------+-----+---------+----------------+ 

ingredient_product

+---------------+---------------------+------+-----+---------+----------------+ 
| Field   | Type    | Null | Key | Default | Extra   | 
+---------------+---------------------+------+-----+---------+----------------+ 
| id   | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| product_id | int(10) unsigned | NO | MUL | NULL |    | 
| ingredient_id | int(10) unsigned | NO | MUL | NULL |    | 
| percentage | tinyint(3) unsigned | NO |  | NULL |    | 
+---------------+---------------------+------+-----+---------+----------------+ 

Answer 1

：

SELECT product_id 
FROM ingredient_product 
WHERE ingredient_id IN (1,2) AND percentage = 50 
GROUP BY product_id 
HAVING COUNT(*) = 2; 

但是如果你需要獨立的百分比，這並不工作，但你可以這樣做：

SELECT product_id FROM 
    (SELECT product_id 
    FROM ingredient_product 
    WHERE ingredient_id = 1 AND percentage = 50 
    UNION ALL 
    SELECT product_id 
    FROM ingredient_product 
    WHERE ingredient_id = 2 AND percentage = 50) AS tmp 
GROUP BY product_id 
HAVING COUNT(*) = 2; 

基本上你添加一個UNION每個要求（由id和百分比組合組成），然後增加HAVING條件的要求數量。

備註：由於要求在這種情況下相互排斥，因此UNION ALL比UNION更快，並且會給出相同的結果。

在子查詢中，您可以使用OR而不是UNION，但我們發現MySQL似乎更喜歡這種格式。然而，不同的版本可能會有所不同。爲了完整起見，在這裏，解決方案，以及：

SELECT product_id 
FROM ingredient_product 
WHERE (ingredient_id = 1 AND percentage = 50) OR (ingredient_id = 2 AND percentage = 50) 
GROUP BY product_id 
HAVING COUNT(*) = 2; 

Answer 2

在假設ID是多餘的，和你有一個完美的維修自然鍵（ product_id，ingredient_id）...

基於草莓答案

SELECT product_id 
    FROM ingredient_product 
WHERE ingredient_id IN (1,2) 
GROUP 
    BY product_id 
HAVING COUNT(*) = 2;