php - 如何在MySQL和PHP中显示所有产品的所有类别？

Question

我是 MySQL 和 PHP 的初学者，我需要你的帮助来了解解决方案。我想显示产品和相关类别的列表。产品和类别是多对多的关系。谷歌的解决方案让我很困惑。我将非常感谢任何建议。

我的代码显示重复的产品。重复次数与类别相同。 例如:

Product1 - Category1;
Product1 - Category2;
Product1 - Category3;
Product2 - Category1;
Product3 - Category3;

index.php:

$result = $pdo -> query('
SELECT product.id, 
       product.name AS product_name, 
       seller.name AS seller_name, 
       category.name AS category_name
  FROM product
  LEFT JOIN seller ON product.sellerid = seller.id
  LEFT JOIN product_category ON product.id = product_category.productid
  LEFT JOIN category ON product_category.categoryid = category.id
');

foreach($result as $row)
{
    $products[] = array(
        'id' => $row['id'], 
        'product_name' => $row['product_name'],
        'seller_name' => $row['seller_name'],
        'category_name' => $row['category_name']
    );
}

index.html.php:

<ul>
    <?php foreach($products as $product): ?>
    <li>
        <span><?php htmlout($product['id']); ?></span>
        <span><?php htmlout($product['product_name']); ?></span>
        <span><?php htmlout($product['seller_name']); ?></span>
        <ul>
            <li>
                <span><?php htmlout($product['category_name']); ?></span>
            </li>
        </ul>
    </li>
    <?php endforeach; ?>
</ul>

如何显示每个产品的所有类别？循环应该是什么样子？我想实现:

Product1 - Category1, Category2, Category3;
Product2 - Category1;
Product3 - Category3;

Answer 1

您可以使用GROUP_CONCAT()获取每行中的所有卖家和类别。

SELECT product.id, product.name,
    GROUP_CONCAT(DISTINCT seller.name) AS sellers,
    GROUP_CONCAT(DISTINCT category.name) AS categories
  FROM product
  LEFT 
  JOIN seller 
    ON product.sellerid = seller.id
  LEFT 
  JOIN product_category 
    ON product.id = product_category.productid
  LEFT
  JOIN category 
    ON product_category.categoryid = category.id
GROUP BY product.id