In this post How to Display Last Login by User in Asp.Net

Important Namespaces Used
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using System.Data;
using System.Data.SqlClient;

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Login Button Click Event
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String mycon = "Data Source=sk-pc;Initial Catalog=LoginDatabase;Integrated Security=True";
        SqlConnection scon = new SqlConnection(mycon);
        String myquery = "select * from LoginDetail where username='" + TextBox1.Text + "'";
        SqlCommand cmd = new SqlCommand();
        cmd.CommandText = myquery;
        cmd.Connection = scon;
        SqlDataAdapter da = new SqlDataAdapter();
        da.SelectCommand = cmd;
        DataSet ds = new DataSet();
        da.Fill(ds);
        String uname;
        String pass;
        String lastlogin;
        if (ds.Tables[0].Rows.Count > 0)
        {
            uname = ds.Tables[0].Rows[0]["username"].ToString();
            pass = ds.Tables[0].Rows[0]["password"].ToString();
            lastlogin = ds.Tables[0].Rows[0]["lastlogin"].ToString();
            scon.Close();

           
            
            


                if (uname == TextBox1.Text && pass == TextBox2.Text)
                {
                       if (lastlogin == "0")
                        {
                            lastlogin = "You Have Logged in Website First Time";
                             Session["firsttime"] = 1;
                         }
                  

                      
                setlastlogin(lastlogin);
                Session["username"] = uname;
                    Session["lastlogin"] = lastlogin;
                    Response.Redirect("MainPage.aspx");
                }
                else
                {
                    Label3.Text = "Invalid Username or Password - Relogin with Correct Username Password- No. of Attemps Remaining : " ;
                   
                }
           }
           
        
        else
        {
            Label3.Text = "Invalid Username or Password - Relogin with Correct Username Password ";

        }

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User Defined Method
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private void setlastlogin(String lastlogin1)
    {
        String mycon = "Data Source=sk-pc; Initial Catalog=LoginDatabase; Integrated Security=True";
        String updatedata = "Update LoginDetail set lastlogin='" + DateTime.Now.ToLongDateString() + " " + DateTime.Now.ToShortTimeString() + "' where username='"+TextBox1.Text+"'";
        SqlConnection con = new SqlConnection(mycon);
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.CommandText = updatedata;
        cmd.Connection = con;
        cmd.ExecuteNonQuery();
    }

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Main Page ( Page Load Coding )
--------------------------------

 if (Session["username"] == null)
        {

            Response.Redirect("Default.aspx");


        }
        else
        {
            Label2.Text = "Welcome " + Session["username"].ToString();
            if (Session["lastlogin"].ToString() == "You Have Logged in Website First Time")
            {
                Label3.Text = "You Have Logged in Website For the First Time";
            }
            else
            {
                Label3.Text = "You Have Last Logged In Website :" + Session["lastlogin"].ToString();
            }

        }

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Logout Button Click Coding
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 Session.Abandon();
        Response.Redirect("Signout.aspx");

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