Question

我想在点击“登录”时检查用户是否存在于数据库中。如果是，则回显“用户存在”，否则“用户不存在”。我怎么能这样做？到目前为止我有：

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

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
     die("Connection failed: " . $conn->connect_error);
} 

?>

<!DOCTYPE html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Test</title>
</head>

<body>
<form method="post" action="login.php">
Username: <input type="text"  value="" name="username" /><br /><br />
Password: <input type="password" value="" name="password" /><br /><br />
<input type="submit" name="submit" value="Log In"/>
</form>
</body>
</html>

Answer 1

试试这个

session_start();
if($_SERVER['REQUEST_METHOD'] === 'POST'){

    $servername = "localhost";
    $username = "root";
    $password = "root";
    $dbname = "test";

// Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    $user = $conn->real_escape_string(htmlspecialchars(trim($_POST['username'])));
    $query = "SELECT `username` FROM `users` WHERE `username` = '$user'";

    $result = $conn->query($query);
    if($result->num_rows > 0) {
       $_SESSION['allowToWelcome'] = true;
       header('Location:welcome.php');
       die();
    }
    else $message = 'user does not exist';

}

?>

    <!DOCTYPE html>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
            <title>Test</title>
        </head>

        <body>
            <form method="post" action="login.php" enctype="multipart/form-data">
                <?php if(isset($message)) : ?>
                    <div class="error"><?php echo $message; ?></div>
                <?php endif; ?>

                Username: <input type="text"  value="" name="username" /><br /><br />
                Password: <input type="password" value="" name="password" /><br /><br />
                <input type="submit" name="submit" value="Log In"/>
            </form>
        </body>
    </html>

在welcome.php中你可以像这样检查

session_start();
if(!isset($_SESSION['allowToWelcome'])){
   header('Location:login.php');
   die();
}

Answer 2

在我制作的登录/注册脚本中，我使用了类似的东西..

// check existing username
$prep_stmt = "SELECT id FROM your-table-name WHERE username = ? LIMIT 1";
$stmt = $mysqli->prepare($prep_stmt);

if ($stmt) {
    $stmt->bind_param('s', $username);
    $stmt->execute();
    $stmt->store_result();

            if ($stmt->num_rows == 1) {
                    // A user with this username already exists
                    $error_msg .= '<p class="error">A user with this username already exists</p>';
                    $stmt->close();
            }
            $stmt->close();
    } else {
            $error_msg .= '<p class="error">Database error line 55</p>';
            $stmt->close();
    }

如何检查SQL数据库中是否存在用户

2 个答案: