Re: idea - new aggregates median, listagg

On Tue, Dec 15, 2009 at 10:28:49PM +0100, Pavel Stehule wrote:
> Hello
> 
> I am looking on new feature - ORDER clause in aggregate, and I thing,
> so we are able to effectively implement some non standard, but well
> known aggregates.
> 
> a) function median - it is relative frequent request - with usually
> slow implementation

Makes a lot of sense.  I suspect we'll have to provide several
different medians, as there are several precise, useful, and
conflicting definitions.  Some examples below:

http://www.simple-talk.com/sql/t-sql-programming/median-workbench/

> b) function listagg (it is analogy of group_concat from MySQL) - it
> should simplify report generating and some other

This is redundant, as it's equivalent to array_to_string(array_agg()).

If it's done as syntactic sugar over that, it's fine.  If it's a
separate implementation, it's a bad idea.  Probably best as an
optional module of some kind.

Cheers,
David.
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