這個問題我的辦法是，使用者有個活躍時間間隔問題。超過這個活躍時間間隔的則可以認為是離線，後者可以登陸，如果無後者登陸，但並不是說前者就需要重新登陸了。因為他的session還在的。只能是這個時間設定的越小越精確，也是不能做到絕對的。
代碼貼出來給樓主參考下。
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,該帳號已在其他地方登陸，網站設定1個ID只能有1個登陸/n你可以稍候嘗試登陸。
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) &)) '刪除x秒沒有活動的訪客
End If
If PrvDbState = True Then DbClose()
End Function