PostgreSQL 8.4 has ANSI SQL:2003 window functions support. These are often classified under the umbrella terms of basic Analytical or Online Application Processing (OLAP) functions.
They are used most commonly for producing cumulative sums, moving averages and generally rolling calculations that need to look at a subset of the overall dataset (a window frame of data) often relative to a particular row.
For users who use SQL window constructs extensively, this may have been one reason in the past to not to give PostgreSQL a second look. While you may not
consider PostgreSQL as a replacement for existing projects because of the cost of migration, recoding and testing, this added new feature is definitely a selling point
for new project consideration.
If you rely heavily on windowing functions, the things you probably want to know most about the new PostgreSQL 8.4 offering are:
What SQL window functionality is supported?
How does PostgreSQL 8.4 offering compare to that of the database you are currently using?
Is the subset of functionality you use supported?
To make this an easier exercise we have curled thru the documents of the other database vendors to distill what the SQL Windowing functionality they provide in their core product.
If you find any mistakes or ambiguities in the below please don't hesitate to let us know and we will gladly amend.
For those who are not sure what this is and what all the big fuss is about, please read our rich commentary on the topic of window functions.