public static void createChallenge(Connection con, int challenged_user, int challenged_by, int quiz_id) throws SQLException {
		String created_on = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")
				.format(Calendar.getInstance().getTime());
		PreparedStatement pStmt = con
				.prepareStatement("INSERT INTO challenges VALUES (NULL, ?, ?, ?, ?)");
		pStmt.setInt(1, challenged_user);
		pStmt.setInt(2, challenged_by);
		pStmt.setInt(3, quiz_id);
		pStmt.setString(4, created_on);
		pStmt.executeUpdate();
	}