QSA = Query String Append.
RewriteRule ^/product/([0-9]*)/? /product.php?product_id=$1 [QSA]
This simply makes the product_id number look like a directory to the user. Now say that I have two different views of the page, view=short and view=long. For whatever reason, I don't want to make these views look like directories by using a RewriteRule. So I want to be able to do things like:
Let's see how QSA works. With QSA, my final rewritten URL is
QSA has caused the RewriteEngine to append the existing query string (view=short) to the new query string (product_id=1351283). Without QSA, the existing query string is simply replaced by the new query string:
If you do much scripting with reliance on GET variables, it is virtually imperative that you enable the QSA flag on all of your RewriteRules. NOTE: I'm not sure how this works with PHP's session identifiers, which can be passed in the URL as a GET variable instead of a session cookie. This would probably be useful to know.