使用PHP检查用户名是否已存在

Question

我想检查我的数据库中是否已存在用户名.如果是,我想重定向回我的注册页面.我的代码用于添加用户名,但不检查用户名是否存在.请帮忙!!!这是register.php页面的代码.代码完全跳过检查"用户名"并插入数据库(如果存在或不存在).

    <?php  
         error_reporting (E_ALL ^ E_NOTICE);    
         include ('dbconn.php');
         session_start();

         $GLOBALS[$error_message];
         $GLOBALS[$username];

         if(isset($_POST['submit']))
           {     
               $error = array();        
               if(empty($_POST['username']))
                 {
                   $error[] = 'Please enter a username. ';
                 }
               else 
                 {
                   $username = mysqli_real_escape_string($connection, $_POST['username']);
                 }

               if(empty($_POST['password']))
                 {
                   $error[] = 'Please enter a password. ';
                 }
               else
                 {
                   $password = mysqli_real_escape_string($connection,$_POST['password']);   
                 }

               if(empty($_POST['cpassword']))
                 {
                   $error[] = 'Please confirm password. ';
                 }
               else
                 {
                   $cpassword = mysqli_real_escape_string($connection,$_POST['cpassword']);
                 }

               if($password == $cpassword)
                 {
                   $mainpassword= $password;
                 }
               else
                 {
                   $error[] = 'Your passwords do not match. ';
                 }      

               if(empty($error))
                 {                     
                   $query = "SELECT * from User WHERE username=' ".$username." ' ";
                   $result = mysqli_query($connection, $query) or die
                       (mysqli_error($connection));

                  if(mysqli_num_rows($result)> 0)
                  {
                   $multi = "Sorry ! This Username is not available...Please choose another";
                  }
                  else{ $sql="INSERT INTO user(username,password)VALUES                          ('$username','$password')";

              mysqli_query($connection, $sql) or die(mysqli_error($connection));
              header('Location:/MySQLi/confirmation.php'); }
}
               else
                  {
                    $error_message = '<span class="error">';
                    foreach($error as $key => $values) {
                    $error_message.="$values";
                    }
                    $error_message.="</span><br/><br/>";    
                    } 
                 }
?>

Answer 1

您正在手动添加用户名周围的空格,以使其看起来不存在:

$query = "SELECT * from User WHERE username=' ".$username." ' ";
                                             ^             ^

应该:

$query = "SELECT * from User WHERE username='".$username."' ";

使用准备好的语句可以一次性避免这个问题和潜在的SQL注入问题:

$query = "SELECT * from User WHERE username=?";

还要确保始终使用表名和列名:User不一定相同user.

另请注意,永远不要将纯文本密码存储在数据库中,应该对它们进行加密和散列.