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;
using System.Data;
namespace SearchingRecord
{
public partial class WebForm1 : System.Web.UI.Page
{
SqlDataAdapter dadapter;
DataSet dset;
string connstring = "server=.;database=emp;user=sa;password=wintellect";
string sql = "select * from emp_detail";

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
dadapter = new SqlDataAdapter(sql, connstring);
dset = new DataSet();
dadapter.Fill(dset);
DropDownList1.DataSource = dset.Tables[0];
DropDownList1.DataTextField = "e_name";
DropDownList1.DataValueField = "e_id";
DropDownList1.DataBind();
GridViewBind();
}
}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
GridViewBind();
}
public void GridViewBind()
{
dadapter = new SqlDataAdapter("select * from emp_detail where e_id=" + DropDownList1.SelectedValue + "", connstring);
dset = new DataSet();
dadapter.Fill(dset);
GridView1.DataSource = dset.Tables[0];
GridView1.DataBind();
}
}
}

Code on .aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="SearchingRecord.WebForm1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<style type="text/css">
.style1
{
height: 3px;
} .style2
{
height: 24px;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<div>
<table style="height: 376px; width: 919px">
<tr>
<td class="style2">
<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
Font-Size="10pt" Height="17px"
onselectedindexchanged="DropDownList1_SelectedIndexChanged" Width="162px">
</asp:DropDownList>
</td>
<td class="style2"></td>
<td class="style2"></td>
</tr>
<tr>
<td class="style1"></td>
<td class="style1"></td>
<td class="style1"></td>
</tr>
<tr>
<td>
<asp:GridView ID="GridView1" runat="server" BackColor="White"
BorderColor="#336666" BorderStyle="Double" BorderWidth="3px" CellPadding="4"
GridLines="Horizontal" Height="168px" Width="452px">
<FooterStyle BackColor="White" ForeColor="#333333" />
<HeaderStyle BackColor="#336666" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#336666" ForeColor="White" HorizontalAlign="Center" />
<RowStyle BackColor="White" ForeColor="#333333" />
<SelectedRowStyle BackColor="#339966" Font-Bold="True" ForeColor="White" />
<SortedAscendingCellStyle BackColor="#F7F7F7" />
<SortedAscendingHeaderStyle BackColor="#487575" />
<SortedDescendingCellStyle BackColor="#E5E5E5" />
<SortedDescendingHeaderStyle BackColor="#275353" />
</asp:GridView>
</td>
<td></td>
<td></td>
</tr>
</table>
</div>
</form>
</body>
</html>

Now run the application.
Output



Select another name from the DropDownList. Like I am selecting a name "SATISH KUMAR".



All records will be shown in the GridView related to "SATISH KUMAR"..

Here are some related resources.

Display Data in GridView Using MySQL

GridView: Delete multiple records using checkbox in asp.net 3.5

Master-detail data-binding using DropDownList in ASP.NET 2.0