检查用户名是否可用

Question

我试图在插入表格之前检查用户名是否可用。

但无论用户名是否已经存在，它似乎都会插入到表中。

这是我的php代码：

<?php
session_start();
define('DB_NAME', 'madsanker_dk_db');
define('DB_USER', 'madsanker_dk');
define('DB_PASSWORD', 'myPassword');
define('DB_HOST', 'mysql43.unoeuro.com');

$link = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD);

if (!$link) {
 die('Could not connect: ' .mysqli_error());
}

$db_selected = mysqli_select_db( $link, DB_NAME);

if (!$db_selected) {
 die('Could not connect: ' .mysqli_connect_error());
}

$username = $_POST['username'];
$password = $_POST['password'];
$name = $_POST['name'];
$email = $_POST['email'];
$username = mysqli_real_escape_string($link,$username);
$password = mysqli_real_escape_string($link,$password);
$name = mysqli_real_escape_string($link,$name);
$email = mysqli_real_escape_string($link,$email);
$password = md5($password);

$sql = "SELECT * FROM mainLogin WHERE username = '$username'";
    
$result = mysqli_query($link, $sql);
    
$count = mysqli_num_rows($result);
if($count > 0) {
$sql = "INSERT INTO mainLogin (username, password, name, email)  VALUES ('$username', '$password', '$name','$email' )";

$result = mysqli_query($link, $sql);

if (!$result) {
 die('Error: ' . mysqli_error($link));
}else {
    $_SESSION['login'] = $username;
  echo "<script>window.location = 'http://madsanker.dk.linux101.unoeuro-server.com'</script>";
}
}else {
    echo "username taken";
}
mysqli_close($link);
?>

我做错了什么？

谢谢！

更新

更改$ count＆gt; 0到$ count == 0工作

Answer 1

只需在“＆gt;”中更改if语句中的更大符号到== 0

if($count==0){

}

Answer 2

如果username已经在db中而不是更改此条件：

if($count > 0) {  
  //your stuff
}

使用：

if($count <= 0) { // if not found
   //your stuff
}