How do you decide what aggregates to add?

hi,

Who decides if a seemingly-useful aggregate is added to Postgres? I
would like to advocate for a couple, but I worry that I'm
misunderstanding some community process that has decided _not_ to add
aggregates or something.

1. I just discovered first()/last() as defined in the wiki [1], where
it's noted that conversion from Access or Oracle is much easier with
them.
2. We use our "homemade" jsonb_object_agg(jsonb) constantly, which is
modeled off of (built-in) json_object_agg(name, value) and (built-in)
jsonb_agg(expression). [2]

Since building these into Postgres (though not fast C versions) is a
matter of a dozen lines of SQL, why haven't they been added already?
Seems like a great thing to brag about in release notes, etc.

Thanks for your thoughts,
Seamus

[1] https://wiki.postgresql.org/wiki/First/last_(aggregate)
[2] http://blog.faraday.io/how-to-aggregate-jsonb-in-postgres/

--
Seamus Abshere, SCEA
https://www.faraday.io
https://github.com/seamusabshere
https://linkedin.com/in/seamusabshere