如何限制同一用户名同时登陆

　　这个问题我的办法是，用户有个活跃时间间隔问题。超过这个活跃时间间隔的则可以认为是离线，后者可以登陆 ，如果无后者登陆，但并不是说前者就需要重新登陆了。因为他的session还在的。只能是这个时间设置的越小越精确，也是不能做到绝对的。
代码贴出来给楼主参考下。
Function CheckOnline() DIM IP,rsPrv,Sql,PrvDbState PrvDbState = False If DBSTATE = False Then DbOpen() PrvDbState = True End If Set rsPrv=Server.CreateObject(ADODB.Recordset) If Session(UserName) = then Sql=select * from [Online] where SessionID=& Session.Sessionid & rsPrv.Open Sql,Conn,1,3 If rsPrv.Eof then rsPrv.AddNew rsPrv(SessionID) = Session.SessionID rsPrv(GroupChargeLv) = -1 rsPrv(LastActTime) = Now() rsPrv(UserIP) = GetIP rsPrv(OnLineTime) = 0 rsPrv(UserWhere) = Request.ServerVariables(HTTP_REFERER) Else rsPrv(UserWhere) = Request.ServerVariables(HTTP_REFERER) rsPrv(OnLineTime) = rsPrv(OnLineTime) + DateDiff(n,rsPrv(LastActTime),Now()) rsPrv(LastActTime) = Now() End If rsPrv.Update rsPrv.Close() response.Write notlogin Else response.Write logined Sql=select * from [Online] where UserName=& Session(UserName) & rsPrv.Open sql,Conn,1,3 If rsPrv.Eof then rsPrv.AddNew rsPrv(SessionID) = Session.SessionID rsPrv(UserName) = Session(UserName) rsPrv(GroupChargeLv) = Session(GroupChargeLv) rsPrv(LastActTime) = Now() rsPrv(OnLineTime) = 0 rsPrv(UserIP)= GetIP rsPrv(UserWhere) = Request.ServerVariables(HTTP_REFERER) Else If rsPrv(SessionID) <> Session.SessionID And Application(LoginSet)(1) = False Then InfoTo LoginOut.asp,该帐户已在其他地方登陆，网站设置1个ID只能有1个登陆\n你可以稍候尝试登陆。 Response.End() End If rsPrv(UserWhere) = Request.ServerVariables(HTTP_REFERER) rsPrv(OnLineTime) = rsPrv(OnLineTime) + DateDiff(n,rsPrv(LastActTime),Now()) rsPrv(LastActTime)=Now() End If rsPrv.Update rsPrv.Close() End If Set rsPrv = Nothing If DateDiff(s,Application(OnLineLastDelete),Now()) > Int(Application(DELETEONLINEDIFF)) Then Application.Lock() Application(OnLineLastDelete) = now Application.UnLock() Conn.ExeCute(delete from [Online] where datedIff(s,LastActTime,Now())>& Int(Application(CHECKONLINEDIFF) &)) 删除x秒没有活动的访客 End If If PrvDbState = True Then DbClose() End Function