我正在为社交网络开发软件,我计划对它进行大量的扩展。实际上,每次用户单击时,我都在更新timestamp列,以确保它们被标记为联机。当他们不点击30秒,他们被标记为离线。SET timestamp = UNIX_TIMESTAMP WHERE uid = 1; -- UNIX_TIEMSTAMP is current unix timestamp given by PHP'sName FROM Users WHERE timestamp > (UNIX_TIMESTAMP - 30); -- (UNIX_TIMESTAMP - 30) is