How to check login time of user from database?

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SQL-Server-2008R2

I want to save login and logout time of user in the databse.I am able to save login time.I want if user has logged in once there should not be duplicate entry on whole particular date. following are my sql coding and c# coding can any one help me..
thanx in advance
my sql table structure is as follows

create table EmpAttendance
(
    AttendenceID int primary key ,
    EmpID nvarchar(10) foreign key references Employee(EmpID),
    LoginTime datetime,
    LogoutTime datetime,
    AttDate datetime
)

And C# coding are..

DataSet ds1 = obj.CheckAttendance(Session["EmpID"].ToString(), (DateTime.Now).ToString());

if (ds1.Tables[0].Rows.Count > 0)
{
    //Response.Write("hiiiiii");
}
else
{
    obj.InsAttendance(Session["EmpID"].ToString(), (DateTime.Now).ToString(), "", (DateTime.Now).ToString());
    // Response.Write("hiiiiii");
}

every time only else part is running.....i want that else part should run only when there is no entry.....


[Edit member="Tadit"]
Added pre tags.
[/Edit]