ASP.NET C#,Javascript - asp.net

Question

Want to populate the second dropdown values based on selection first of first drop down.
id Bankname Branchname
1 HDFC AMT
2 HDFC gag
3 icic AMsfsaT
4 bpjn daD
in the first drop down if I select the HDFC then in second dropdown AMT,gag should come.
I am using following code to fill first dropdown.
string com = "Select * from mst_bank";
SqlDataAdapter adpt = new SqlDataAdapter(com, con);
DataTable dt = new DataTable();
adpt.Fill(dt);
ddlbank.DataSource = dt;
ddlbank.DataBind();
ddlbank.DataTextField = "Bankname";
ddlbank.DataValueField = "ID";

Answer 1

Add 2 DropDownLists:
<asp:DropDownList ID="ddl1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl1_SelectedIndexChanged" /><br />
<asp:DropDownList ID="ddl2" runat="server" />
And your code behind will be:
private string conStr = WebConfigurationManager.ConnectionStrings["YourConnectionString"].ConnectionString;
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
FillDDL1();
FillDDL2(ddl1.SelectedValue);
}
}
protected void FillDDL1()
{
SqlConnection con = new SqlConnection(conStr);
SqlCommand cmd = new SqlCommand("Select * from mst_bank", con);
try
{
con.Open();
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
sda.Fill(ds);
ddl1.DataSource = ds;
ddl1.DataTextField = "Bankname";
ddl1.DataValueField = "ID";
ddl1.DataBind();
}
catch (Exception ex)
{
//work with exception
}
finally
{
con.Close();
}
}
protected void ddl1_SelectedIndexChanged(object sender, EventArgs e)
{
FillDDL2(ddl1.SelectedValue);
}
protected void FillDDL2(string id)
{
SqlConnection con = new SqlConnection(conStr);
SqlCommand cmd = new SqlCommand("Select * from second_table where BANK_ID = #id", con);
cmd.Parameters.Add("#id", SqlDbType.Int).Value = id;
try
{
con.Open();
SqlDataAdapter sda = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
sda.Fill(ds);
ddl1.DataSource = ds;
ddl1.DataTextField = "Name";
ddl1.DataValueField = "ID";
ddl1.DataBind();
}
catch (Exception ex)
{
//work with exception
}
finally
{
con.Close();
}
}
On PostBack we fill dropdown1 and dropdown2, using corresponding value from the dropdown1. Method ddl1_SelectedIndexChanged will be occur when user changes selection, and dropdown2 will be filled with a corresponding values. Of course, you have to change a SQL-query there.