Albe Laurenz wrote: > Thomas Munro wrote: >> I am using 9.1.6, and I've set up a partitioned table as described >> in the manual, with partitions based on a timestamptz column >> called 'time'. The exclusion constraints work nicely when I select >> ranges of times with literal constants. But why would a WHERE >> clause like the following not benefit from exclusion constraints? >> >> time > TIMESTAMPTZ '2012-11-03 00:00:00Z' + INTERVAL '24 hours' >> >> >> Isn't that expression on the right reducible to a constant up >> front? Obviously I can use a host language to do the arithmetic >> and provide a constant, but I am curious to understand why that >> wouldn't be constant-folded. > > I think the problem is that this + operator is implemented > by the function "timestamptz_pl_interval", which is STABLE > but not IMMUTABLE. > > I am not sure why this function cannot be IMMUTABLE, it > seems to me that it should be. For TIMESTAMP WITHOUT TIME ZONE it couldn't be IMMUTABLE, because the result would be based on the time zone setting of the client connection; but adding a fixed interval to a UTC time to get a UTC time seems pretty immutable to me. That said, I'm not sure why STABLE wouldn't be good enough for such an optimization, if it were supported at all. I don't think we evaluate such expressions before developing the plan, though. If you run EXPLAIN ANALYZE on one of the queries involved, does it actually perform the scan of partitions which can be skipped at run-time, or does it show "never executed"? -Kevin -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
