On Tue, Jun 25, 2013 at 12:08:34PM -0400, Tom Lane wrote: > Bruce Momjian <br...@momjian.us> writes: > > I looked at predtest.c but I can't see how we accept >= and <= ranges, > > but not CHECK (a % 16 == 3). It is the '%' operator? I am not sure why > > the hashme() function is there. Wouldn't it work if hashme() was an > > immutable function? > > No. Robert's description is exactly correct: it's a question of whether > we can know that the semantics of function X have anything to do with > the behavior of operator Y. In the case of something like CHECK (X >= 16) > combined with WHERE X = 10, if the given = and >= operators belong to > the same btree opclass family then we can assume that their semantics > are compatible and then apply reasoning to show that these two clauses > can't both be true for the same value of X. We can *not* use "X = 10" > to reason about the behavior of anything that isn't in the = operator's > btree opclass, because we don't assume that "=" means "absolutely > identical for every purpose". And in fact it does not mean that for > several pretty common datatypes (float being another example besides > numeric).
OK, so it is really the index comparisons that we are using; makes sense. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
