Ideally, you would have a calendar table to join your data table. If you don't, you can build one on the fly with a CTE similar to a tally or numbers table.
Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?
How to post data/code on a forum to get the best help: Option 1 / Option 2