Обсуждение: Exclusion constraint with negated operator?
Hi,
I wanted to create an exclusion constraint like
EXCLUDE (c1 WITH =, c2 with <>)
This gives an error:
operator <>(integer,integer) is not a member of operator family "integer_ops"
I can resolve that by using gist and the btree_gist extension.
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?
We have a ton of overlap operators (geometric, ranges, arrays) but none for the opposite. Sometimes that's useful for exclusion constraints.
Thanks,
Torsten
=?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