PHP技术开发中遇到的常见问题及解决方法

echo "Hello, world!";

$x = 10;
$y = 20

echo $x + $y;

// 错误：缺少分号

// 普通循环
for ($i = 0; $i < 10000; $i++) {
    echo $i;
}

// 优化后的循环
for ($i = 0; $i < 100; $i++) {
    for ($j = 0; $j < 100; $j++) {
        echo $i * 100 + $j;
    }
}

// 重复查询数据库
for ($i = 0; $i < 10; $i++) {
    $result = queryFromDatabase();
    echo $result;
}

// 使用缓存技术
$data = null;
for ($i = 0; $i < 10; $i++) {
    if ($data == null) {
        $data = queryFromDatabase();
    }
    echo $data;
}

// 示例1：未处理用户输入
$username = $_GET['username'];
$passWord = $_GET['password'];
$sql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
$result = queryFromDatabase($sql);

// 示例2：使用参数化查询
$username = $_GET['username'];
$password = $_GET['password'];
$sql = "SELECT * FROM users WHERE username = ? AND password = ?";
$stmt = $conn->prepare($sql);
$stmt->bind_param("ss", $username, $password);
$stmt->execute();
$result = $stmt->get_result()->fetch_all(MysqlI_ASSOC);

// 示例3：转义特殊字符
$username = $_GET['username'];
$password = $_GET['password'];
$username = mysqli_real_escape_string($conn, $username);
$password = mysqli_real_escape_string($conn, $password);
$sql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
$result = queryFromDatabase($sql);

// 未处理用户输入
$username = $_GET['username'];
echo "欢迎您，" . $username;

// 处理用户输入
$username = $_GET['username'];
$username = htmlspecialchars($username);
echo "欢迎您，" . $username;