使用PHP连接MySQL数据库的多种方及错误处理

<?php
$servername = "localhost";  // 数据库服务器地址
$username = "root";        // 数据库用户名
$password = "";            // 数据库密码
$dbname = "test";          // 数据库名称

// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);

// 检查连接状态
if (!$conn) {
    die("连接失败: " . mysqli_connect_error()); // 输出错误信息并终止脚本
}
echo "连接成功";

// 关闭连接（可选，脚本结束会自动关闭）
mysqli_close($conn);
?>

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test";

// 创建连接对象
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接状态
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}
echo "连接成功";

// 关闭连接
$conn->close();
?>

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test";

try {
    // 创建PDO实例
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    
    // 设置错误模式为异常捕获
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "连接成功";
} catch(PDOException $e) {
    echo "连接失败: " . $e->getMessage(); // 捕获并输出异常信息
}

// 关闭连接（置为null即可）
$conn = null;
?>

if (!$conn) {
    die("错误代码: " . mysqli_connect_errno() . "，详细信息: " . mysqli_connect_error());
}

try {
    // 连接代码
} catch (PDOException $e) {
    echo "错误信息: " . $e->getMessage();
}

$stmt = $conn->prepare("SELECT * FROM users WHERE email = ?");
$stmt->bind_param("s", $email);
$stmt->execute();

$sql = "SELECT id, name FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
    }
} else {
    echo "0 结果";
}

try {
    $conn->beginTransaction();
    // 执行多条SQL
    $conn->exec("UPDATE accounts SET balance = balance - 100 WHERE user_id = 1");
    $conn->exec("UPDATE accounts SET balance = balance + 100 WHERE user_id = 2");
    $conn->commit();
} catch (Exception $e) {
    $conn->rollBack();
    echo "事务失败: " . $e->getMessage();
}