registration form not not showing validation error - php

Question

I am having issues getting the error to appear when a user is entering a user name that is already taken.
In the code below the database is updated when successful entry is made. However, when an entry is made with a duplicate user name, the entry is placed in the database and no error message is shown. I have looked on the net and tried a few methods and this what I have so far. Thank you for taking a look :)
<?php
// Create connection
$con = mysqli_connect('172.16.254.111', "user", "password", "database"); //(connection location , username to sql, password to sql, name of db)
// Check connection
if (mysqli_connect_errno($con)) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
} //sql syntax below, first line is collumn titles on the db and second line is values from the html document
//$_post is a form of sending information in php
{
$username = strip_tags($_POST['username']);
$password = md5(strip_tags($_POST['pass']));
$password2 = md5(strip_tags($_POST['pass2']));
$fullname = strip_tags($_POST['fullname']);
$email = strip_tags($_POST['email']);
$department = strip_tags($_POST['department']);
if ($password != $password2) //password doestn equal same as password 2 then the message below is displayed (working)
{
echo "<H2>password doesn't match</H2>";
}
$usercheck = "SELECT * FROM Users WHERE username=$username";
$usercheck2 = mysql_query($usercheck);
if (mysql_fetch_assoc($usercheck2)) {
echo "<H2>This username already exists, please pick another</H2>";
} else {
$sql = "INSERT INTO Users(username, password, password2, email, fullname, department)
VALUES('$username','$password','$password2','$email','$fullname','$department')";
if (!mysqli_query($con, $sql)) {
die('Error: ' . mysqli_error($con));
}
echo "<H2>Registration was successful, please use the access console above</H2>";
}
}
?>
Excuse any comments in the code; I am a beginner at PHP and coding in general.

Answer 1

You're missing some quotes. Try this:
$usercheck = "SELECT * FROM Users WHERE username = '$username'";
// ----------------------------------was missing---^---------^
$usercheck2 = mysql_query($usercheck);
if (mysql_num_rows($usercheck2)) {
echo 'user exists';
}
Also, you shouldn't be using the mysql_* functions. Look into using PDO

Answer 2

Change $usercheck = "SELECT * FROM Users WHERE username=$username";
for this $usercheck = "SELECT * FROM Users WHERE username='$username'"; And tell me if it works.