Exporting GridView to Excel

In this code snippet, I will show how you can export data from a GridView control to a Microsoft Excel spreadsheet.
The Code
Listing 1: Default.aspx

Listing 2: Default.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
BindData();
}
}

private void BindData()
{
string query = "SELECT * FROM Categories";
SqlConnection myConnection = new SqlConnection(ConnectionString);
SqlDataAdapter ad = new SqlDataAdapter(query, myConnection);
DataSet ds = new DataSet();
ad.Fill(ds, "Categories");
GridView1.DataSource = ds;
GridView1.DataBind();
}

private string ConnectionString
{
get { return @"Server=localhost;Database=NorthWind;Trusted_Connection=true"; }

}
protected void BtnExport_Click(object sender, EventArgs e)
{
Response.Clear();
Response.AddHeader("content-disposition", "attachment;filename=FileName.xls");
Response.Charset = "";

// If you want the option to open the Excel file without saving then
// comment out the line below
// Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.ContentType = "application/vnd.xls";
System.IO.StringWriter stringWrite = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
GridView1.RenderControl(htmlWrite);
Response.Write(stringWrite.ToString());
Response.End();
}

In the above listing, the GridView control will be populated with the data from the Categories table of the Northwind database. You will have to give the appropriate Server name or IP instead of localhost as server name in the above connection string.
If you use this code and try to export the GridView control, you will see an error message saying that the GridView control must be placed inside the form tags with the runat = server attribute.
This is pretty confusing, since your GridView is already inside the form tags and also contains the runat = server attribute. You can easily resolve this error by adding the following lines.
Listing 3: Overiding VerifyRenderingInServerForm Method
public override void VerifyRenderingInServerForm(Control control)
{
/* Confirms that an HtmlForm control is rendered for the specified ASP.NET
server control at run time. */
}
Yup, that’s it. Now, when you click the button, the GridView control will be exported correctly. It will prompt you either to open the file as it is or to save it elsewhere.

Updating table using row_number() over (order by columnName)

--Create temp table
create table #temptable
(
col1 int,
col2 int,
col3 int
)
--insert three values
insert into #tempTable values (1,2,3)
insert into #tempTable values (1,2,3)
insert into #tempTable values (1,2,3)
--update value based on row_number() over (order by columnName)
update temp
set col3=3
from
(
select row_number() over(order by col1) as row_id,* from #tempTable
)temp
where row_id =2
--View Updated Data
select * from #tempTable