Hello
I did task from TODO: Add BETWEEN ASYMMETRIC/SYMMETRIC.
SELECT 2 BETWEEN 1 AND 5 -> true
SELECT 2 BETWEEN 5 AND 1 -> false
SELECT 2 BETWEEN SYMMETRIC 5 AND 1 -> true
this patch is based on Robert's B. Easter work from 2001 year.
http://archives.postgresql.org/pgsql-patches/2001-01/msg00022.php
it's trivial, only small change in parser.
Best regards
Pavel Stehule