Query String Parameters

     Query String Parameters are used to pass values from one page to another page. Query String parameters are created by using the ? symbol at the end of the url while navigating to a page. Next to ? symbol, specify the parameter nae followed by = operator followed by the value to pass using that parameter. When you have multiple parameters then separate them with & symbol. 

          

                      Server.Transfer("~/page2.aspx?pname=value&pname=value")

To read Query String parameters, use query string property of Request object.

                      Varname=Request.QueryString["pname"]

The following example creates two pages Querystring1.aspx and Querystring2.aspx and withen the 1st page within a gridveiw the details of departments are displayed with select option and when user select a department then the selected deptno will be passed to 2nd page through querystring parameter and within the second page the list of employeees working in that deptnowill be displayed in a gridveiw.

1.  Add a page to the website with the name querystring1.aspx, take a gridview on it, set the id of that gridveiw to Gvdept, set its AutoGenerateSelectButton property to true

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;

namespace WebApp
{
    public partial class Querystring1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            SqlConnection cn = new SqlConnection("server=localhost; database=db1;uid=cheryl;trusted_connection=true");
            SqlCommand cmd = new SqlCommand("Select * from dept", cn);
            cn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            gvdept.DataSource = dr;
            gvdept.DataBind();
            gvdept.DataKeyNames = new string[] { "Deptno" };
            cn.Close();
            dr.Close();
        }
        protected void gvdept_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
        {
            gvdept.SelectedIndex = e.NewSelectedIndex;
            string Dno = gvdept.SelectedValue.ToString();
            Response.Redirect("~/Querystring2.Aspx?Dno=" + Dno);
        }
    }
} 

2.  Add another page to the website with the name querystring2.aspx. Place a gridveiw on that page, set its id as GvEmp

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;

namespace WebApp
{
    public partial class Querystring2 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            string Dno = Request.QueryString["Dno"].ToString();
            string Sql = "Select * from emp where Deptno=" + Dno;
            SqlConnection cn = new SqlConnection("server=localhost; database=db1;uid=cheryl;trusted_connection=true");
            SqlCommand cmd = new SqlCommand(Sql, cn);
            cn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            gvemp.DataSource = dr;
            gvemp.DataBind();
            cn.Close();
            dr.Close();

        }
    }
}