Problem With Simple Sqlclient Database Acces

This is a part of my project and that are my first steps. I just want to know if there is a user with "username" already in the database. The MSDN Documentation says that the ExecuteNonQuery() Method returns the number of affected rows. But if I run this code I always get x=-1. What does that mean ?


using (SqlConnection sqlcon = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["web_db_1"].ConnectionString))
        {
            SqlCommand cmd = new SqlCommand("Select user_id From users Where username = '" + username + "'", sqlcon);
            cmd.CommandType = CommandType.Text;
            cmd.Connection.Open();
            int x = cmd.ExecuteNonQuery();
            cmd.Connection.Close();
        }

 Thanks,

Party-Pansen