MySQL php从数据库获取项目并以XML形式存储（重复项目）

首先，这里是我的代码，它是有效的，只是有一个主要的缺陷，我不知道如何修复。为了更好地阅读，我已经清除了所有元素的代码，除了那些导致问题的元素

    $servername = "localhost";
    $username = DB_USERNAME;
    $password = DB_PASSWORD;
    $database = DB_DATABASE;

    // Start of table variables

    // End of table variables
    // Create connection
    $conn = new mysqli($servername, $username, $password, $database);

    $sql = "SELECT pd.name as product_name, p.model as product_model, p.quantity as product_quantity, cd.name as category_name , p.product_id as product_id , p.price as product_price , m.name as product_manufacturer ,  p.image as product_image , pd.description as product_description
            FROM product p
            INNER JOIN product_description pd ON pd.product_id = p.product_id
            INNER JOIN product_to_category ptc ON ptc.product_id = p.product_id
            INNER JOIN category_description cd ON cd.category_id = ptc.category_id
            INNER JOIN manufacturer m ON m.manufacturer_id = p.manufacturer_id
            WHERE pd.language_id = 2 AND cd.language_id = 2 AND p.status = 1 AND p.product_id = p.product_id AND p.manufacturer_id = p.manufacturer_id";

    $conn->set_charset('utf8mb4');
    $result = $conn->query($sql);

    $xml = new XMLWriter();

    $xml->openURI("php://output");
    $xml->startDocument();
    $xml->setIndent(true);

    $xml->startElement('products');

    if ($result->num_rows > 0) {
        while ($product = $result->fetch_assoc()) {
            $product_id             = $product["product_id"];
            $product_category       = $product["category_name"];

                $xml->startElement("product");

                    $xml->startElement("itemid");
                        $xml->writeRaw($product_model);
                    $xml->endElement();


                    $xml->startElement("category");
                        $xml->writeCDATA($product_category);
                    $xml->endElement();
                    //end

                $xml->endElement();

        }
    }else{

    }

    $xml->endElement();

    $xml->flush();

?>

当我运行代码时，一切都开始了，它生成了XML结构。我在下面发布的XML是第一个ID为23793的产品

代码复制了我的产品3次，因为每个产品都有一个主类游戏、子类PS3和子类战斗

我怎样才能使它不会重复同一个产品3次，但对于产品23793，可以获得游戏>PS3>战斗等类别

我试着在类别上做一个foreach循环，但我不认为它来自php，但问题来自MySQL选择代码

有什么想法吗？

您需要在查询中添加GROUP\u CONCAT

选择 pd.name作为产品名称， p、 模型作为产品模型， p、 数量作为产品数量， 组\u CONCATcd.name分隔符“>”作为类别\u名称， p、 产品标识作为产品标识， p、 价格作为产品价格， m、 作为产品制造商的名称， p、 形象作为产品形象， 产品描述作为产品描述 来自产品p 内部连接产品描述pd上的pd.product\U id=p.product\U id 在ptc.product\U id=p.product\U id上将产品\U内部连接到类别ptc 内部连接类别\u说明cd上的cd.category\u id=ptc.category\u id 内部连接m上的制造商m.manufacturer\u id=p.manufacturer\u id 哪里 pd.language_id=2 和cd.language_id=2 p.status=1 p.product\u id=p.product\u id p.manufacturer\u id=p.manufacturer\u id 按产品编号分组 试试这个：

select case when@var <> brand then @Var :=p.product_id end as product_id
(
SELECT pd.name as product_name, p.model as product_model, p.quantity as product_quantity, cd.name as category_name , p.product_id as product_id ,     p.price as product_price , m.name as product_manufacturer ,  p.image as product_image , pd.description as product_description
FROM product p
INNER JOIN product_description pd ON pd.product_id = p.product_id
INNER JOIN product_to_category ptc ON ptc.product_id = p.product_id
INNER JOIN category_description cd ON cd.category_id = ptc.category_id
INNER JOIN manufacturer m ON m.manufacturer_id = p.manufacturer_id
WHERE pd.language_id = 2 AND cd.language_id = 2 AND p.status = 1 AND     p.product_id = p.product_id AND p.manufacturer_id = p.manufacturer_id
GROUP BY p.product_id
)
as foo
cross join (Select @var := '') as foo2

---

您可以在顶部选择中添加所需的其他字段，但这将基本上消除第一个字段中产品的重复。

请您详细解释一下GROUP_CONCAT是什么？in基本上将数据行组合并为单个字符串。可能更容易理解。但是不管怎样，想知道新的查询是否有帮助？你也需要在查询中添加一个p.product_id分组。谢谢@rob-我通过在where子句中选择一个产品id进行了测试，并通过以下方式对分组进行了检查：@LucasKrupinski工作得很有魅力，你是deseve爵士奖牌，太棒了，你能用synax解释这个分组吗？

product_id | category_id

   23793   |  58  (This is the ID of Games)
   23793   |  135 (This is the ID of PS3)
   23793   |  777 (This is the ID of Fighting)

select case when@var <> brand then @Var :=p.product_id end as product_id
(
SELECT pd.name as product_name, p.model as product_model, p.quantity as product_quantity, cd.name as category_name , p.product_id as product_id ,     p.price as product_price , m.name as product_manufacturer ,  p.image as product_image , pd.description as product_description
FROM product p
INNER JOIN product_description pd ON pd.product_id = p.product_id
INNER JOIN product_to_category ptc ON ptc.product_id = p.product_id
INNER JOIN category_description cd ON cd.category_id = ptc.category_id
INNER JOIN manufacturer m ON m.manufacturer_id = p.manufacturer_id
WHERE pd.language_id = 2 AND cd.language_id = 2 AND p.status = 1 AND     p.product_id = p.product_id AND p.manufacturer_id = p.manufacturer_id
GROUP BY p.product_id
)
as foo
cross join (Select @var := '') as foo2