And maybe not on the wall, but instead in your SQLz, eating your data. But a bit more seriously. Ever since PostgreSQL 8.4 we have window functions, but still I see people which do not know it or are wary to ...
On 15th of December Tom Lane committed patch by Andrew Gierth (aka RhodiumToad), which adds interesting capability: Log Message: ----------- Support ORDER BY within aggregate function calls, at long last providing a non-kluge method for controlling the order in which values are fed to ...
Finally, we got very important addons to PostgreSQL, which help with dealing with arrays. It solves a lot of problems, which were usually solved with standard cookbook code, which was in faqs, blog posts and number of examples on irc.