Window function in the CVS HEAD (8.4) !

Window function (SQL 2003) - one of the very interesting for OLAP feature previously missed in PostgreSQL was committed to the CVS HEAD by Tom Lane. Hitoshi Harada wrote proposal and made a patch, see his site for more details. There was no support for user-defined window function, but Tom believe, that 8.4 should have it. Very good.

Simply speaking, window function is an aggregate over a partitioned set of rows. Think about window moving over rows.

One of the interesting application of window function would be data smoothing.