Today, on irc, someone asked interesting question. Basically she ran a query like: select a, b, c, d, e, f from table order by a then, she processed the query to get, for each a array of unique values of b, c, d, ...

On 23rd of December, Tom Lane committed patch: Support ordered-set (WITHIN GROUP) aggregates. This patch introduces generic support for ordered-set and hypothetical-set aggregate functions, as well as implementations of the instances defined in SQL:2008 (percentile_cont(), percentile_disc(), rank(), dense_rank(), percent_rank(), cume_dist()). We also added mode() ...