C# - Using Multiple Sql Queries On Single Button Click

protected void Button2_Click(object sender, EventArgs e)
{
String a = DropDownList1.SelectedItem.Value;
String b = DropDownList3.SelectedItem.Value.PadLeft(3, '0');
String c = TextBox2.Text.PadLeft(5,'0').ToString();
String d = TextBox3.Text.ToString();
String digit = a+ b + c + d;
try
{
myConn = new OdbcConnection("Driver={MySQL ODBC 3.51 Driver};Server=localhost;Database=testcase;User=root;Password=root;Option=3;");
myConn.Open();
//**
string sql = "select * from testcase.main where reg_no =?";
//**
OdbcCommand cmd = new OdbcCommand(sql, myConn);
//**
cmd.Parameters.AddWithValue("?", digit);
MyReader = cmd.ExecuteReader();
//**
while (MyReader.Read())
{
String f = MyReader["pet_name"].ToString();
String g = MyReader["res_name"].ToString();
Label9.Visible = true;
Label9.Text = f;
Label10.Visible = true;
Label10.Text = "VS";
//Label11.Visible = true;
Label11.Text = g;
}
MyReader.Close();
}
catch (Exception e1)
{
Response.Write(e1.ToString());
}
finally
{
if (MyReader != null && !MyReader.IsClosed)
{
MyReader.Close();
}
if (myConn != null && myConn.State == ConnectionState.Open)
{
myConn.Close();
}
}

I want to add another sql query which is using two tables to fetch the data and than i want to display it in a dropdownlist after fetching data from database. How should i proceed?? Should i create a totally new connection? I tried many different ways like, creating new connection and new reader and entire try and catch block i coded again but on running the website i t was taking very long to load the contents. What i did i modified only this portion(below code) and used the entire try catch again but it dint work.

while (MyReader1.Read())
{
String f = MyReader1["ret"].ToString();
DropDownList1.Items.Add(f);
}