SQL PHP按多列分组

SELECT customer_id, product_id, SUM(quantity) AS total_quantity
FROM orders
GROUP BY customer_id, product_id;

<?php
// 连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 执行SQL查询
$sql = "SELECT customer_id, product_id, SUM(quantity) AS total_quantity
        FROM orders
        GROUP BY customer_id, product_id";
$result = $conn->query($sql);

// 处理查询结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "客户ID: " . $row["customer_id"]. " - 产品ID: " . $row["product_id"]. " - 总数量: " . $row["total_quantity"]. "<br>";
    }
} else {
    echo "没有结果";
}

// 关闭数据库连接
$conn->close();
?>