php - 检查用户名是否已存在于数据库中

Question

我试图验证注册表单中的用户名字段并检查所选用户名是否已存在于数据库中但未按预期工作。我不确定如何解决这个问题。这是来源

$query = "SELECT * FROM users WHERE username = :username";
$sq = $pdo->prepare($query);
$sq->execute(array(
         ':username'    => $username                                
        ));
$res=$sq->fetch();
if (!$res) {
    echo ' Database Error Occured ';
}
else { echo "username already exist in database"; }

if ($res === 0) {
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->beginTransaction();
    try 
    {
         $sql = "INSERT INTO users ( username, password, email, path)
                            VALUES (:username, :password, :email, :path)";

                $q = $pdo->prepare($sql);
                $q->execute(array(
                    ':username' => $username,
                    ':password' => $password,
                    ':email'    => $email,
                    ':path'     => $path                                
                    ));                 

                $lastInsertID = $pdo->lastInsertId();
                $sql = $pdo->prepare("UPDATE users SET level=:user_id WHERE user_id=:user_id");
                $sql->execute(array(
                    ':user_id'  => $lastInsertID
                    ));
                $pdo->commit();     
     }

发生的事情是当我点击提交按钮时如果我输入了存在的用户名我得到了用户名已经存在于数据库中但是如果我输入了另一个不存在的用户名我得到了发生数据库错误

Answer 1

if(1 < $res->rowCount()){
    print('username already exist');
}