如何使用php和mysql计算单循环中多个表的月度和？

$servername = "数据库服务器地址";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名称";

// 使用MySQLi连接数据库
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

// 使用PDO连接数据库
try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e) {
    die("连接数据库失败: " . $e->getMessage());
}

$tables = array("table1", "table2");
$sum = 0;

foreach ($tables as $table) {
    $sql = "SELECT SUM(value) AS total FROM $table WHERE MONTH(date) = $month";
    $result = $conn->query($sql);
    
    if ($result->num_rows > 0) {
        $row = $result->fetch_assoc();
        $sum += $row["total"];
    }
}

echo "月度总和为: " . $sum;

$conn->close();  // MySQLi关闭连接
// 或
$conn = null;    // PDO关闭连接