Appending to a QueryString

[Freelve]

Imagine you have a menu with categories. Each of which contains a link to the parent page, but with a querystring. For instance:\[code\]<a href="http://stackoverflow.com/questions/12591870/?category=5">Category 5</a>\[/code\]This shows some items for category 5 in a gridview. Now I want to have the ability to sort said gridview, also using a querystring. So the querystring I should end up with is:\[code\]?category=5&sortby=namedesc\[/code\]But I wouldn't know what category was already chosen. So I'd have to take the existing querystring and add &sortby=namedesc. Now if I were to choose another category from the menu, the querystring should of course not add a new "&category=" but change the existing one accordingly.The only way I've figured out how to do this is to make them into link buttons and in the "onclick" analyze the existing querystring, and append/change values as needed. Then doing\[code\]Request.Redirect("page.aspx" + newQueryString);\[/code\]This should work, but it seems a highly inefficient way of doing this as it will require 2 postbacks for each click.My question is: Is there a smarter/better way of handling this?