mysql - 不知何故无法防止名称重复

Question

我最近在注册系统上遇到了一些问题，我尝试了很多方法来防止名称重复，并且已经浏览了 stackoverflow。 但我似乎无法找到解决方案。

这是我的代码

 <?php
    if (isset($_POST['registerBtn']))
    {
        $username = $_POST['username'];
        $password = $_POST['password'];
        $rpassword = $_POST['rpassword'];
        $email = $_POST['email'];
        $errors = array();
        $checkUsername = $odb -> prepare("SELECT COUNT(*) as total from FROM `users` WHERE `username` = :username");
        $checkUsername -> execute(array(':username' => $username));
        $countUsername = $checkUsername -> fetchColumn(0);
        if ($checkUsername > 0)
        {
            $errors['Username is already taken'];
        }
        if (!ctype_alnum($username) || strlen($username) < 4 || strlen($username) > 15)
        {
            $errors[] = 'Username Must Be  Alphanumberic And 4-15 characters in length';
        }
        if (!filter_var($email, FILTER_VALIDATE_EMAIL))
        {
            $errors[] = 'Email is invalid';
        }
        if (empty($username) || empty($password) || empty($rpassword) || empty($email))
        {
            $errors[] = 'Please fill in all fields';
        }
        if ($password != $rpassword)
        {
            $errors[] = 'Passwords do not match';
        }
        if (empty($errors))
        {
            $insertUser = $odb -> prepare("INSERT INTO `users` VALUES(NULL, :username, :password, :email, 0, 0, 0, 0)");
            $insertUser -> execute(array(':username' => $username, ':password' => SHA1($password), ':email' => $email));
            echo '<div class="nNote nSuccess hideit"><p><strong>SUCCESS: </strong>User has been registered.  Redirecting....</p></div><meta http-equiv="refresh" content="3;url=login.php">';
        }
        else
        {
            echo '<div class="nNote nFailure hideit"><p><strong>ERROR:</strong><br />';
            foreach($errors as $error)
            {
                echo '-'.$error.'<br />';
            }
            echo '</div>';
        }
    }
    ?>

Answer 1

您可以这样对用户名设置UNIQUE 约束:

CREATE TABLE users
(
    id int NOT NULL AUTO_INCREMENT,
    username varchar(30),
    password varchar(80),
    email varchar(80),
    PRIMARY KEY (id),
    UNIQUE KEY username (username)
)