Thread: BUG #5852: Function date_trunc is not IMMUTABLE
The following bug has been logged online: Bug reference: 5852 Logged by: Oleg Email address: serovov@gmail.com PostgreSQL version: 8.3 Operating system: CentOS Description: Function date_trunc is not IMMUTABLE Details: Please mark function date_trunc as IMMUTABLE for using in index. Thanks!
On Thu, Jan 27, 2011 at 11:02:46AM +0000, Oleg wrote: > > The following bug has been logged online: > > Bug reference: 5852 > Logged by: Oleg > Email address: serovov@gmail.com > PostgreSQL version: 8.3 > Operating system: CentOS > Description: Function date_trunc is not IMMUTABLE > Details: > > Please mark function date_trunc as IMMUTABLE for using in index. it cannot be immutable. please check explanation in here: http://www.depesz.com/index.php/2010/09/09/why-is-my-index-not-being-used/ search for "immutable". Best regards, depesz -- Linkedin: http://www.linkedin.com/in/depesz / blog: http://www.depesz.com/ jid/gtalk: depesz@depesz.com / aim:depeszhdl / skype:depesz_hdl / gg:6749007
"Oleg" <serovov@gmail.com> writes: > Please mark function date_trunc as IMMUTABLE for using in index. The version for timestamp without time zone already is marked immutable. The version for timestamp with time zone can't be marked immutable, because it isn't: its behavior depends on the timezone setting. Depending on what it is you hope to accomplish, you might be able to do something like this: regression=# create table t1 (f1 timestamptz); CREATE TABLE regression=# create index ii on t1 (date_trunc('day', f1 AT TIME ZONE 'UTC')); CREATE INDEX This is immutable because the truncation happens with respect to a fixed timezone. (Doesn't have to be UTC, any constant timezone name will do.) regards, tom lane