返回SQL语句的有关问题

try
        {
            try
            {
                brand = Request.QueryString["brand"].Trim();
                price = Request.QueryString["price"].Trim();
                graphics = Request.QueryString["graphics"].Trim();
                size = Request.QueryString["size"].Trim();
            }
            catch (Exception exone)
            {
                
            }
            DataConn Conn = new DataConn();
            if (brand == "" && price == "" && size == "" && graphics == "")
            {
                sql = "select * from TB_Laptop";
                Response.Write("<script>alert('!!!')</script>");
            }
            else
            {
                Response.Write("<script>alert('!!!')</script>");
                try
                {
                    sql = "select * from TB_Laptop where Type='laptop'";
                    if (brand != "")
                        sql += " and SearchBrand='" + brand + "'"; //从这里开始后面的就不执行了。。  
                    Response.Write("<script>alert('1" + sql + "')</script>");
                    if (price != "")
                        sql += " and SearchPrice='" + price + "'";
                    Response.Write("<script>alert('2" + sql + "')</script>");
                    if (size != "")
                        sql += " and SearchSize='" + size + "'";
                    Response.Write("<script>alert('3" + sql + "')</script>");
                    if (graphics != "")
                        sql += " and SearchGraphics='" + graphics + "'";
                    Response.Write("<script>alert('4" + sql + "')</script>");
                }
                catch (Exception extwo) {
                    Response.Write("<script>alert('" + extwo.Message + "')</script>");
                }
            }
            Response.Write("<script>alert('!!!')</script>");
            Conn.ExcuteSearch(sql);
            DT = new DataTable();
            DT = Conn.MyDT;
            if (DT.Rows.Count < 1)
            {
                Response.Write("<script>alert('抱歉，我们暂时还未收录您所筛选的商品！感谢您对我们的支持！')</script>");
            }
            else
            {
                DataList1.DataSource = DT;
                DataList1.DataBind();
            }
        }
        catch (Exception ex) {
            Response.Write("<script>alert('"+ex.Message+"')</script>");
        }