我想检查一个用户名是否已经存在于我的数据库中。如果是的话，我想重定向回我的注册页面。我的代码可以添加用户名，但不检查用户名是否存在。请救命！！！这是register.php页面的代码。代码完全跳过对'username'的检查，并将其插入到数据库中（如果它存在或不存在）。
<?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/>";
}
}
?>
您正在手动在用户名周围添加空格,这样用户名看起来就像不存在：
$query = "SELECT * from User WHERE username=' ".$username." ' ";
^ ^
应该是：
$query = "SELECT * from User WHERE username='".$username."' ";
使用准备好的语句可以一次性避免该问题和潜在的sql注入问题：
$query = "SELECT * from User WHERE username=?";
还要确保一致使用表名和列名:user不一定与user相同。
还要注意，您不应该将纯文本密码存储在数据库中，您应该对它们进行salt和hash。
