Attendance Management system project

Question

I have an employee name textbox and a login button when i click on login buton for a user only once the current date with empname should be stored in SQL SERVER I NEED THE LOGIC

 

private void btn_itLogin_Click(object sender, EventArgs e)

{

//if(txt_iwdEname.Text!="")

// {

//DateTime dt = new DateTime();

//dt = DateTime.Now;

selectQueryString = "insert into tb_empInTime(Emname,Empindate,Empintime) values('" +

txt_iwdEname.Text + "','" + DateTime.Now + "','"+DateTime.Now+"')";

ExecQuery();

MessageBox.Show("You have Logged in \n Have a nice day", txt_iwdEname.Text, MessageBoxButtons.OK, MessageBoxIcon.Information);

// }

}

else

{

MessageBox.Show("You have already logged in", "Alert", MessageBoxButtons.OK, MessageBoxIcon.Error);

}

 

By this code i am getting a user login info multiple times per day i need only once