=?UTF-8?Q?Torsten_F=C3=B6rtsch?= <tfoertsch123@gmail.com> writes:
> My question is can I somehow express something like
> EXCLUDE (c1 WITH =, c2 with NOT =)
> It seems that's not possible at the moment. But is there any obstacle in
> principle or is it just not implemented?
Well, it'd likely be a bad idea. Indexes are meant to help you quickly
find a small part of a table that satisfies a condition. Finding the
probably-much-larger part of the table that doesn't satisfy the condition
is something they are bad at. This is why "=" is an indexable operator
while "<>" is not. It's not impossible in principle for "<>" to be an
index operator, but the set of cases where indexing on such a condition
would beat a seqscan is likely to be uselessly small. By the same
token, EXCLUDE constraints using such a condition would be unpleasantly
inefficient.
regards, tom lane