I tried: CREATE INDEX blocks_created_at_timezone_idx ON blocks USING btree ((created at time zone timezone));
(Actually, I originally did try one on "(created at time zone timezone)::date" but couldn't figure out how to phrase it in a way PostgreSQL would accept.)
Anyway, no difference: http://explain.depesz.com/s/Zre
I even tried changing the filter to (created at time zone timezone) > 'yesterday' AND (created at time zone timezone) < 'today' to see if that might make a difference. Sadly, no: http://explain.depesz.com/s/dfh
Here's the definition for the offending table:
CREATE TABLE blocks
(
block_id character(24) NOT NULL,
user_id character(24) NOT NULL,
created timestamp with time zone,
locale character varying,
shared boolean,
private boolean,
moment_type character varying NOT NULL,
user_agent character varying,
inserted timestamp without time zone NOT NULL DEFAULT now(),
networks character varying[],
lnglat point,
timezone character varying,
CONSTRAINT blocks_pkey PRIMARY KEY (block_id )
)
WITH (
OIDS=FALSE
);
CREATE INDEX blocks_created_at_timezone_idx
ON blocks
USING btree
(timezone(timezone::text, created) );
CREATE INDEX blocks_created_idx
ON blocks
USING btree
(created DESC NULLS LAST);
CREATE INDEX blocks_lnglat_idx
ON blocks
USING gist
(lnglat );
CREATE INDEX blocks_moment_type_idx
ON blocks
USING btree
(moment_type );
CREATE INDEX blocks_networks_idx
ON blocks
USING btree
(networks );
CREATE INDEX blocks_private_idx
ON blocks
USING btree
(private );
CREATE INDEX blocks_shared_idx
ON blocks
USING btree
(shared );
CREATE INDEX blocks_timezone_idx
ON blocks
USING btree
(timezone );
On Thu, Feb 9, 2012 at 11:46 AM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Alessandro Gagliardi <alessandro@xxxxxxxx> writes:
> WHERE ... (created at time zone timezone)::date = 'yesterday'
The only way to make that indexable is to create an _expression_ index on
> created has an index (btree if it matters). timezone does not. I'm
> wondering if the solution to my problem is to create a joint index between
> created and timezone (and if so, if there is a particular way to do that to
> make it work the way I want).
the whole _expression_ "(created at time zone timezone)::date". Seems
pretty special-purpose, though it might be worthwhile if you do that a
lot.
regards, tom lane
