I have to use query string passed in url to some link.

Question

I have edit as hyperlink in which i have to pass sid and flag value as query string.But I have to used query string already in url in my link How I will pass flag value.

<Columns>
               <asp:BoundField DataField="sid" HtmlEncode="false" DataFormatString="<a target='_blank' href='bsepsu.aspx?sid={0}&flag={}'>Edit</a>" />

           </Columns>