How to rewrite SEO friendly url's like stackoverflow

Question

If you go to a url like the following: http://stackoverflow.com/questions/9155602/ the address bar will be updated to http://stackoverflow.com/questions/9

Answer 1

for duplicate content, you should have a canonical link tag in the head. the canonical link tag will tell google that the current page has an alternate url for the same content as the canonical link, and the main url for this content is the canonical link. this is great for things like paginated content, searches, ect where the same page could have different urls.