登录用户系统有关问题。为什么Red返回总是为0~

if ((this.usertxt.Text == "") || (this.pwdtxt.Text == ""))        {            Response.Write("<script>alert('用户名、密码不能为空');</script>");        }        else        {            string ConnectionString = "server=localhost;database=user;uid=sa;pwd=123456";            SqlConnection con = new SqlConnection(ConnectionString);            con.Open();            string name = this.usertxt.Text.ToString();            string pass = this.pwdtxt.Text.ToString();            string cmdtxt = "select * from vip where user='" + name  + "' and pwd ='" + pass + " '";                        SqlCommand cmd = new SqlCommand(cmdtxt, con);            int red = Convert.ToInt32(cmd.ExecuteScalar());            if (red > 0)            {                Session["admin_name"] = this.usertxt.Text.ToString();                Response.Redirect("hello.aspx");            }            else            {                Response.Write("<script>alert('请与管理员联系！');</script>");            }        }