Reason: As a non-dba, I can’t install additional modules like first_last_agg.
For what it's worth, I support the inclusion of first() and last() in the main release. It makes queries involving multiple aggregate functions a lot simpler. Most hosted services only allow official contrib modules.
Related questions pop up on Stackoverflow every now and then.
(I don't see anything related in the Postgres Todo, yet.)
The implementation in the additional module first_last_agg looks very simple and straight-forward. Might be an easy task to incorporate into mainline Postgres. But my C foo is just not good enough to judge whether the implementation is ideal.
