Introduction :
  Hi, here i will code you how to Create and Download the Excel sheet using C# and Asp.net the Data of    Excel sheet will be loaded from Database.

Logic :
  Here i have created a Dummy Gridview, values from the Database will bind into the dummy Grid, and later   Create the Excel sheet and Write Grid Data to the Excel and Render it.

Aspx code :
<html>
<head runat="server">
<title>Fourthbottle</title>
</head>
<body style="text-align:center">
<form id="form1" runat="server">
Click to Create and Download Excel,Excel Data from DB.
<div>
<asp:Button ID="btnClick" runat="server" Text="Create" onclick="btnClick_Click" />
</div>
</form>
</body>

</html>

Code behind (C#) :
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Text;

namespace DBTOEXCEL
{
public partial class Page1 : System.Web.UI.Page
{
SqlConnection con = new SqlConnection("your Conn String");
protected void btnClick_Click(object sender, EventArgs e)
{
DataTable dt = new DataTable();
SqlDataAdapter da = new SqlDataAdapter("select * from table1", con);
con.Open();
da.Fill(dt);
con.Close();
GridView gv = new GridView();
gv.DataSource = dt;
gv.DataBind();
Response.Clear();
Response.AddHeader("content-disposition","attachment;filename=ExcelDownload.xls");
Response.ContentType = "application/vnd.ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(sw);
gv.RenderControl(hw);
Response.Output.Write(sw.ToString());
Response.End();
}
}

}