Question

这是我的代码。一切都很完美。它可以防止用户名重复。我已经遇到的唯一问题是当已经注册的用户再次尝试注册时回显“用户已经存在”。

<!DOCTYPE html>
<html>
 <head>
 <meta charset="utf-8">
 <title>Registration</title>
 <link rel="stylesheet" href="style2.css" />
  </head>
  <body>
  <?php
   $con = mysqli_connect("localhost","root","","register");

  if (mysqli_connect_errno()) {
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
 }

 if (isset($_REQUEST['username'])){

     $username = stripslashes($_REQUEST['username']);
     $username = mysqli_real_escape_string($con,$username); 

     $password = stripslashes($_REQUEST['password']);
     $password = mysqli_real_escape_string($con,$password);

     $query = "INSERT into `users` (username, password) 
     VALUES ('$username', '".md5($password)."')";

     $result = mysqli_query($con,$query);

    if($result){
        echo "<div class='form'>
       <h3>You are registered successfully.</h3>
       <br/>Click here to <a href='login.php'>Login</a></div>";
        }
     }else{
  ?>
 <div class="form">
   <h1>Registration</h1>
   <form name="registration" action="" method="post">

   <input type="text" name="username" placeholder="Username" required />
   <input type="password" name="password" placeholder="Password" required />
   <input type="submit" name="submit" value="Register" />
 </form>
  </div>
 <?php } ?>
</body>
</html>

Answer 1

这应该有效，问题是你在插入另一个之前没有检查用户名是否存在。你会在我的代码中看到我评论它。

不要使用md5加密密码，因为它不安全，请使用password_hash（）和password_verify（）函数。

<?php

$con = mysqli_connect("localhost", "root", "", "register");

if (mysqli_connect_errno())
{
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
}


// if is pressed submit button ( Register )
if (isset($_POST['submit']))
{

    $username = stripslashes($_POST['username']);
    $username = mysqli_real_escape_string($con, $username); 

    $password = stripslashes($_POST['password']);
    $password = mysqli_real_escape_string($con, $password);

    // check if username already exists
    $q = mysqli_query($con, "SELECT username FROM users WHERE username = '$username'");
    $user_exists = mysqli_num_rows($q);

    // if number of rows is grateater that 0 it's mean that username exists
    if ($user_exists > 0)
    {
        echo "Username in use, please select another one.";
    }
    else
    {
        // if username don't exists
        $query = "INSERT INTO users (username, password) VALUES ('$username', '".md5($password)."')";

        $result = mysqli_query($con,$query);

        if($result)
        {
          echo "<div class='form'>
                  <h3>You are registered successfully.</h3>
                  <br/>Click here to <a href='login.php'>Login</a>
                </div>";
        } 
    }


}

?>

<!DOCTYPE html>
<html>
  <head>
      <meta charset="utf-8">
      <title>Registration</title>
      <link rel="stylesheet" href="style2.css" />
  </head>
  <body>

  <div class="form">
    <h1>Registration</h1>
      <form name="registration" action="" method="post">
        <input type="text" name="username" placeholder="Username" required />
        <input type="password" name="password" placeholder="Password" required />
        <input type="submit" name="submit" value="Register" />
      </form>
  </div>

</body>
</html>

Answer 2

在插入之前运行像

这样的查询

SELECT * FROM `users`  WHERE `username` = '$username'

然后检查用户是否已经存在并采用一些安全的访问数据库的方式，即pdo

Answer 3

您需要计算表行以检查用户名是否已存在

     $count = "SELECT COUNT(username) as count FROM table WHERE username = '$username'";

 $result = mysqli_query($count);
 $users = mysqli_fetch_assoc($result);

 $numrows = $users['username'];

 If ($numrows == 1) {
    Echo "your message";
 }

回声用户已经存在

3 个答案: