PHP能为您做什么？详细介绍PHP的功能特点

<?php
echo "<h1>欢迎访问我们的网站！</h1>";
?>

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_POST['name'];
    $email = $_POST['email'];
    // 处理表单数据
}
?>

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

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("数据库连接失败：" . $conn->connect_error);
}

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

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

$conn->close();
?>

<?php
session_start();

$_SESSION['user_id'] = 123;
$_SESSION['username'] = 'John';

echo "欢迎，" . $_SESSION['username'];
?>

<?php
$file = fopen("example.txt", "r") or die("无法打开文件！");
echo fread($file, filesize("example.txt"));
fclose($file);
?>