How To Return True If A Sql Row Exists

 Hi all,
 I am trying to access a sql database and if the userid exists in the database to the let me query another statement within an IF block to check another statement within the data, however I cannot seem to get it to work. I need something like sql.row.count != 0 within  the 2nd IF statement below. What can I do?

Thanks in advance.
Jason

 
  
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
       
    }
    protected void btnStart_Click(object sender, ImageClickEventArgs e)
    {
        if (Session["userid"] == null)
        {
            Response.Redirect("accessdenied.aspx");
        }
        else
        {
            //Response.Redirect("page1.aspx");
            SqlConnection objConnect = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["MyConnection"].ConnectionString);

            objConnect.Open();
            SqlCommand cmd = new SqlCommand("SELECT user_id FROM users WHERE user_id = '" + Session["userid"] + "'");

            if (cmd == true)
            {
                Response.Redirect("page5.aspx");
            }

            objConnect.Close();
        }
    }
}