PHP choose another username - php

Question

I have made a registration PHP file that runs through an authentication and connects to my database that I made in phpMyAdmin. The problem is, I can put in the same username without consequence and it adds to the database, so I could put; dogs as the username and then again put the same.
How can I make it so the user is told; that username already exists choose another one.
Here's my php so far;
Also please tell me where to insert it.
<?php
require('db.php');
// If form submitted, insert values into the database.
if (isset($_POST['username'])) {
$username = $_POST['username'];
$email = $_POST['email'];
$password = $_POST['password'];
$username = stripslashes($username);
$username = mysql_real_escape_string($username);
$email = stripslashes($email);
$email = mysql_real_escape_string($email);
$password = stripslashes($password);
$password = mysql_real_escape_string($password);
$trn_date = date("Y-m-d H:i:s");
$query = "INSERT into `users` (username, password, email, trn_date) VALUES ('$username', '".md5($password)."', '$email', '$trn_date')";
$result = mysql_query($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 {
?>

Answer 1

You should query the database before inserting any record (user) to users table.
Try the code below:
<?php
$username = mysql_real_escape_string( $username ); //Sql injection prevention
$existance = mysql_query("SELECT username FROM users WHERE username = '" . $username . "'");
if( !$existance ){
$query = "INSERT into `users` (username, password, email, trn_date) VALUES ('$username', '".md5($password)."', '$email', '$trn_date')";
$result = mysql_query( $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{
//unsuccessful insertion
}
} else {
//the user existed already, choose another username
}
?>

Answer 2

Create an if-statement where you check if $username exists in the db. If it does, throw an error. If not, continue with the code.
Note
Your code is vulnerable to SQL-injection. Read this post: How can I prevent SQL injection in PHP?

Answer 3

Rewriting my entire answer to a working example. I'm going to assume your post variables are the same as mine: email, password, username
<?php
$errorMessage = "";
function quote_smart($value, $handle) {
if (get_magic_quotes_gpc()) {
$value = stripslashes($value);
}
if (!is_numeric($value)) {
$value = "'" . mysql_real_escape_string($value, $handle) . "'";
}
return $value;
}
$email = $_POST['email'];
$password = $_POST['password'];
$username = $_POST['username'];
$email1 = $_POST['email'];
$username1 = $_POST['username'];
$password1 = $_POST['password'];
$email = htmlspecialchars($email);
$password = htmlspecialchars($password);
$username = htmlspecialchars($username);
$connect = mysql_connect("localhost","DBuser", "DBpassword");
if (!$connect) {
die(mysql_error());
}
mysql_select_db("DBName");
$results = mysql_query("SELECT * FROM users WHERE username = '$username'");
while($row = mysql_fetch_array($results)) {
$kudots = $row['username']; }
if ($kudots != ""){
$errorMessage = "Username Already Taken";
$doNothing = 1;
}
$result = mysql_query("SELECT * FROM users WHERE email = '$email'");
while($row2 = mysql_fetch_array($results)) {
$kudots2 = $row2['email']; }
if ($kudots2 != ""){
$errorMessage = "Email Already in use";
$doNothing = 1;
}
//test to see if $errorMessage is blank
//if it is, then we can go ahead with the rest of the code
//if it's not, we can display the error
if ($errorMessage == "") {
$user_name = "DBUsername";
$pass_word = "DBPassword";
$database = "DBName";
$server = "localhost";
$db_handle = mysql_connect($server, $user_name, $pass_word);
$db_found = mysql_select_db($database, $db_handle);
if ($db_found) {
$email = quote_smart($email, $db_handle);
$password = quote_smart($password, $db_handle);
$username = quote_smart($username, $db_handle);
if ($username1 == ""){
$errorMessage = "You need a username";
}
if ($password1 == ""){
$errorMessage = $errorMessage . "<br>You need a password.";
}
if (!(isset($_POST['email']))){
$errorMessage = $errorMessage . "<br>You need an email.";
}
$SQL = "SELECT * FROM users WHERE email = $email";
$result = mysql_query($SQL);
$num_rows = mysql_num_rows($result);
if ($num_rows > 0) {
$errorMessage = "email already exists";
$doNothing = 1;
}
if ($errorMessage == "") {
$SQL = "INSERT INTO users (email, username, password) VALUES ($email, $username, $password)";
$result = mysql_query($SQL);
mysql_close($db_handle);
//=================================================================================
// START THE SESSION AND PUT SOMETHING INTO THE SESSION VARIABLE CALLED login
// SEND USER TO A DIFFERENT PAGE AFTER SIGN UP
//=================================================================================
session_start();
$_SESSION['email'] = "$email1";
$_SESSION['password'] = "$password1";
header ("Location: myaccount.php");
else {
$errorMessage = "Database Not Found";
}
}
OK, now echo $errorMessage right below or above the form, to inform the user that the Email, or Username is taken. I'm pretty sure I have a duplicate function in here for the Email, but this code does work; disregard if somebody says it's vulnerable to SQL injection; this is a working EXAMPLE! If you want to do MySQL real escape string, just Google it. I had to rewrite a couple things because I don't want my full code on a public board, if for some odd reason this doesn't work; send me an eMail(canadezo121#gmail.com) and I'll send you the full page code. (Which WORKS!) This code will probably raise some concerns with other more professional coders, this example gives you a good logical viewpoint of what goes on and how it works. You can adjust it to MySQLi, PDO, etc as you get more familiar with PHP and MySQL.

Answer 4

1 you must verify if the username all ready exists in database (Select)
2 if not exists after you can insert the new user