如何在php中执行sql查询

<?php
try {
    $dsn = 'mysql:host=localhost;dbname=testdb;charset=utf8';
    $username = 'your_username';
    $password = 'your_password';

    $pdo = new PDO($dsn, $username, $password);

    // SELECT 查询
    $stmt = $pdo->query('SELECT * FROM users');
    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
        echo $row['username'] . '<br>';
    }

    // INSERT 查询
    $stmt = $pdo->prepare('INSERT INTO users (username, email) VALUES (:username, :email)');
    $stmt->bindParam(':username', 'newuser');
    $stmt->bindParam(':email', 'newuser@example.com');
    $stmt->execute();

} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}
?>

<?php
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "testdb";

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

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

// SELECT 查询
$sql = "SELECT * FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo $row["username"] . "<br>";
    }
} else {
    echo "0 results";
}

// INSERT 查询
$sql = "INSERT INTO users (username, email) VALUES ('newuser', 'newuser@example.com')";
if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>