Players Online 1 or 0/NULL

[Sigoles]

Hello, how I do to put 1 in colum "online" when X player is online and 0/NULL if offline?
PS. I'm online and there is "NULL" ...

iologindata.cpp

void IOLoginData::updateOnlineStatus(uint32_t guid, bool login)
{
    if (g_config.getBoolean(ConfigManager::ALLOW_CLONES)) {
        return;
    }

    std::ostringstream query;
    if (login) {
        query << "INSERT INTO `players_online` VALUES (" << guid << ')';
    } else {
        query << "DELETE FROM `players_online` WHERE `player_id` = " << guid;
    }
    Database::getInstance()->executeQuery(query.str());
}