mysqli数据库工具类

$mysqli = new mysqli("localhost", "username", "password", "database");
if ($mysqli->connect_error) {
    die("连接失败: " . $mysqli->connect_error);
}
echo "连接成功";

$stmt = $mysqli->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $username);
$username = $_POST['username'];
$stmt->execute();
$result = $stmt->get_result();

$mysqli->begin_transaction();
try {
    $mysqli->query("UPDATE users SET balance = balance - 100 WHERE id = 1");
    $mysqli->query("UPDATE users SET balance = balance + 100 WHERE id = 2");
    $mysqli->commit();
} catch (Exception $e) {
    $mysqli->rollback();
    echo "事务失败: " . $e->getMessage();
}