Question

我有3个表，产品，类别和couple_product_category 我希望数据库中的所有产品都包含一系列耦合类别。但是，当我添加一个尚未与类别相关联的新产品时，这种方式可以正常工作。

我想要最快的方法来阻止性能。这就是我现在所拥有的：

SELECT 
   product.id, 
   product.product_name, 
   GROUP_CONCAT(productcategory.name SEPARATOR '; ') AS categories
FROM
   m_catalog_products AS product
LEFT JOIN 
   couple_product_category AS category
ON 
   category.product_id = product.id
INNER JOIN 
   m_catalog_productcategoy AS productcategory
ON 
   productcategory.id = category.category_id
GROUP BY 
   product.id
ORDER BY product.id, product.is_active ASC

这将导致类似：

ID  Name       Categories
--  ---------  ----------------------
1   Product A  Category A; Category B
2   Product B  Category C

但是，如果产品C尚未与任何类别相关联，则应显示如下：

ID  Name       Categories
--  ---------  ----------------------
1   Product A  Category A; Category B
2   Product B  Category C
3   Product C

Answer 1

LEFT JOIN m_catalog_productcategoy代替INNER JOIN：

SELECT 
   p.id, 
   p.product_name, 
   GROUP_CONCAT(pc.name SEPARATOR '; ') AS categories
FROM m_catalog_products AS p
LEFT JOIN couple_product_category AS c ON c.product_id = p.id
LEFT JOIN m_catalog_productcategoy AS pc ON pc.id = c.category_id
GROUP BY  p.id
ORDER BY p.id, p.is_active ASC;

显示带有类别的产品列表不会显示未耦合的类别

1 个答案: