Form should show alert if duplicate username
<p>ive created a form and im using php to check if the username exists in the database, if it is then the form will not submit and echo an alter that the username has already been taken, if i fill the form out and submit it with a name thatn i know is in the database, i get the error saying that the username already exists, but i also get the text that says.. Thank you for signing up</p>

<p>basically its showing the error correctly but it still submitting all the for data to the database</p>

<p>can you see anything in my code thats causing this??</p>

<pre><code>//Check to see if the username is already taken
$query = "SELECT * FROM clients";
$result = mysql_query($query) or die(mysql_error()); // Get an array with the clients
while($row = mysql_fetch_array($result)){ // For each instance, check the username
if($row["username"] == $username){
    $usernametaken = true;
}else{$usernametaken = false;}
}

// If the username is invalid, tell the user.
// Or else if the password is invalid, tell the user.
// Or else if the email or PayPal address is invalid, tell the user.
// Else, if everything is ok, insert the data into the database and tell
// the user they’ve successfully signed up.

if($usernametaken)
{
echo "That username has been taken.";
}

if(!preg_match('/^[a-zA-Z0-9]+$/', $username ))// If our username is invalid
{
echo "The username can only contain letters or numbers";    // Tell the user
}
 else if(!preg_match('/^[a-zA_Z0-9]+$/', $password ))// If our password is invalid
{
echo "The password can only contain letters or numbers";    // Tell the user
}
// If our email or PayPal addresses are invalid

else if(!preg_match("/^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,3})$/", $email))
 {
 return "The email or PayPal address you entered is invalid."; // Tell the user
 }
 else{

// Inserts the data into the database
$result = mysql_query("INSERT INTO clients (client_ID, username, password, email, paypal)"."VALUES ('', '$username', '$pw', '$email', '$paypal')"); 

echo "Thank you for signing up.";
}

?&gt;
</code></pre>
