Currently it's unsafe/not possible to use some funtions, like
date_trunc, in immutable functions and expression indexes.
It'd be really useful to have an immutable version that took the
timezone as an argument. Maybe this is a worthwhile beginner TODO item
for the wiki?
I'm sure there are other funcs that could use TimeZone-insensitive
variants too.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services