获取所有产品Id，但在php mysql中一次获取一个产品Id

// 连接到MySQL数据库
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 查询数据库中的产品ID
$sql = "SELECT product_id FROM products";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 循环输出每个产品ID
    while($row = $result->fetch_assoc()) {
        $product_id = $row["product_id"];
        echo "产品ID: " . $product_id . "<br>";
    }
} else {
    echo "没有找到任何产品ID";
}

// 关闭数据库连接
$conn->close();