Php交易不起作用

Question

选择查询工作正常但插入命令没有将数据保存在数据库中，我认为我没有正确完成事务，或者由于语法使用不当而可能是滚动支持事务

session_start();
if (isset($_COOKIE['username'])) {
$_SESSION['role'] = $_COOKIE['role'];
$_SESSION['username'] = $_COOKIE['username'];
$_SESSION['rid'] = $_COOKIE['rid'];
}
if (!isset($_SESSION['username'])) {
header('location: login.php');
}

$servername = "localhost";
$username = "johnalla_Mohsin";
$password = "Mohsin1982";
$database = "johnalla_m_billing";

// Create connection
$conn = new mysqli($servername, $username, $password, $database);

date_default_timezone_set('Asia/Karachi');
$currentdate = date("Y-m-d");

// Check connection

if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}

if (isset($_COOKIE['username'])) {

$_SESSION['role'] = $_COOKIE['role'];
$_SESSION['username'] = $_COOKIE['username'];
$_SESSION['rid'] = $_COOKIE['rid'];
}

if (isset($_POST['invoice_no'])) {
$conn->autocommit(FALSE);
$result1 = $conn->query("select sum(cost * quantity) as total from temp_entries");
if ($result1->num_rows > 0) {
    // output data of each row
    while ($row1 = $result1->fetch_assoc()) {
        $total = $row1["total"];
    }
    if ($conn->query("insert into bill (c_name, date, total) values ('$_POST[name]', '$_POST[date]', '$total')") === TRUE) {
        $last_id = $conn->insert_id;
        $result2 = $conn->query("select * from temp_entries");
        if ($result2->num_rows > 0) {
            // output data of each row
            while ($row2 = $result2->fetch_assoc()) {
                $entries[] = $row2;
                $conn->query("insert into bill_entries (bill_id, item_name, description, cost, quantity) "
                        . "values ('$last_id', '$row2[item_name]', '$row2[description]', '$row2[cost]', '$row2[quantity])");
            }
            if ($conn->query("truncate table temp_entries") === TRUE) {
                $conn->commit();
            }
        }
    } else {
        echo "Error: " . $sql . "<br>" . $conn->error;
    }
}
$conn->close();