如何在Mysqli查询中将行转换为列

<?php
// 连接到MySQL数据库
$mysqli = new mysqli("localhost", "username", "password", "database");

// 检查连接是否成功
if ($mysqli->connect_errno) {
    echo "Failed to connect to MySQL: " . $mysqli->connect_error;
    exit();
}

// 构建查询语句
$query = "SELECT category, SUM(quantity) AS total_quantity
          FROM your_table
          GROUP BY category";

// 执行查询
$result = $mysqli->query($query);

// 检查查询是否成功
if (!$result) {
    echo "Query failed: " . $mysqli->error;
    exit();
}

// 将查询结果转换为关联数组
$data = array();
while ($row = $result->fetch_assoc()) {
    $data[$row['category']] = $row['total_quantity'];
}

// 输出转换后的结果
foreach ($data as $category => $total_quantity) {
    echo "Category: " . $category . ", Total Quantity: " . $total_quantity . "<br>";
}

// 释放结果集和数据库连接
$result->free();
$mysqli->close();
?>