checking username against database pdo - php

Question

The script works to add user data into the db however I want the check if the username is in use but keep running into this error
Fatal error: Call to a member function rowcount() on a non-object in /home/4507408/public_html/registeruser.php on line 78
I cant seem to manage to do it with PDO, any help would be great!
<?php
$form = $_POST;
$username = $form[ 'username' ];
$password = $form[ 'password' ];
$firstname = $form[ 'firstname' ];
$location = $form[ 'location' ];
$age = $form[ 'age' ];
$email = $form[ 'email' ];
$usercheck = $_POST['username'];
$check = "SELECT username FROM use WHERE username = '$usercheck'";
$query = $DBH->prepare( $check );
$query = $DBH->prepare($check);
$query->execute();
$data = $query->fetchALL();
$check2 = $check->rowcount();
//if the name exists it gives an error
if ($check2 != 0) {
die('Sorry, the username '.$_POST['username'].' is already in use.');
}
$sql = "INSERT INTO user ( username, password, firstname, location, age, email ) VALUES ( :username, :password, :firstname, :location, :age, :email )";
$query = $DBH->prepare( $sql );
?>

Answer 1

This line:
$check = "SELECT username FROM use WHERE username = '$usercheck'";
is wrong. use is a SQL reserved word. I assume you meant user. It's also a terrible idea to inject a value into the query string with simple variable substitution. The whole point of PDO is to use parametrized queries: http://us1.php.net/pdo.prepared-statements