Question

我有两张桌子：

1. products
- product_id
- title
2. product_categories
- product_id
- category_id

每种产品可以有多个类别。我将此信息存储在product_categories表中。我希望能够在1个查询中选择产品时选择所有category_ids。我怎样才能做到这一点？到目前为止我有以下内容，但它只会选择1个类别ID：

SELECT
  p.*,
  (SELECT
     category_id
   FROM 
     product_categories
   WHERE product_id = p.product_id) as category_ids
FROM
   products AS p

Answer 1

选择产品。*，product_categories来自 product_categories.product_id = products.product_id

左外连接product_categories

Answer 2

您可以使用左连接，分组依据和GROUP_CONCAT

How to use GROUP BY to concatenate strings in MySQL?

SELECT products.*, GROUP_CONCAT(category_id SEPARATOR ' ')
FROM products LEFT JOIN product_categories
                ON product_categories.product_id = products.product_id
GROUP BY product_id;

每行选择一个数组？

2 个答案: