A long overdue post about new functionality. At this moment it is no longer such new, as it was committed on 28th of December (yes, I know, I should have written it earlier, Sorry).
On this day Tom Lane committed patch by Hitoshi Harada which adds support for so called window functions:
Support window functions a la SQL:2008. Hitoshi Harada, with some kibitzing from Heikki and Tom.