MySQL/PHP按行值合并行

SELECT grade, GROUP_CONCAT(name) AS names, AVG(age) AS average_age
FROM students
GROUP BY grade;

// 连接MySQL数据库
$conn = mysqli_connect("localhost", "username", "password", "database");

// 查询需要合并的数据
$query = "SELECT grade, name, age FROM students";
$result = mysqli_query($conn, $query);

// 定义一个空数组用于存储合并后的结果
$mergedRows = array();

// 遍历结果集
while ($row = mysqli_fetch_assoc($result)) {
    $grade = $row['grade'];
    $name = $row['name'];
    $age = $row['age'];

    // 如果数组中已存在该年级的数据，则将姓名合并到对应的数组元素中
    if (isset($mergedRows[$grade])) {
        $mergedRows[$grade]['names'] .= ', ' . $name;
    } else {
        // 如果数组中不存在该年级的数据，则创建一个新的数组元素
        $mergedRows[$grade] = array(
            'names' => $name,
            'average_age' => $age,
        );
    }
}

// 输出合并后的结果
foreach ($mergedRows as $grade => $data) {
    echo "年级：{$grade}\n";
    echo "姓名：{$data['names']}\n";
    echo "平均年龄：{$data['average_age']}\n";
    echo "\n";
}