public boolean checkUniqueNickname(String nickname){
		boolean isUnique = false;
		try {
			Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
			String url = "jdbc:derby:" + DBName;
			Connection connection = DriverManager.getConnection(url);
			Statement statement = connection.createStatement();
			String sqlStatement = "SELECT * FROM users WHERE jnick='" + nickname + "'";
			ResultSet rs = statement.executeQuery(sqlStatement);
			isUnique = !rs.next();
			statement.close();
			connection.close();
		} catch (Exception e) {
			new ServerResultFrame(e.getMessage());
		}
		return isUnique; 
	}