如何使用PHP的group来统计mysql？

<?php
// 连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 执行查询
$sql = "SELECT column_name, COUNT(*) as count FROM table_name GROUP BY column_name";
$result = $conn->query($sql);

// 处理结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "列名: " . $row["column_name"]. " - 统计数量: " . $row["count"]. "<br>";
    }
} else {
    echo "没有结果";
}

// 关闭连接
$conn->close();
?>