public static boolean isUserFree(String email, String username) throws ESellException
	{
		makeConnection();
    	PreparedStatement preparedStatement = null;
    	
        if(conn != null)
        {
            try {
            	//Statement vorbereiten
                String sql = "SELECT * FROM users WHERE email = ? OR username = ?";
                preparedStatement = conn.prepareStatement(sql);
                preparedStatement.setString(1, email);
                preparedStatement.setString(2, username);
                
                //Statement absetzen
                ResultSet result = preparedStatement.executeQuery();
                return !result.next();
                	
            } catch (SQLException e) {
                e.printStackTrace();
                throw new ESellException(ESellException.ErrorCode.DB_ERR);
            }
        }
        else
        	throw new ESellException(ESellException.ErrorCode.DB_ERR);
	}