php验证用户名是否存在

<?php
// 假设我们有一个数据库连接
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

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

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

// 获取用户输入的用户名
$inputUsername = $_POST['username'];

// 查询数据库
$sql = "SELECT * FROM users WHERE username = '$inputUsername'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    echo "用户名已存在";
} else {
    echo "用户名可用";
}

$conn->close();
?>

<?php
// 使用预处理语句防止SQL注入
$stmt = $conn->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $inputUsername);
$stmt->execute();
$result = $stmt->get_result();

if ($result->num_rows > 0) {
    echo "用户名已存在";
} else {
    echo "用户名可用";
}

$stmt->close();
$conn->close();
?>