From: | Patrick Dung <patrick_dkt(at)yahoo(dot)com(dot)hk> |
---|---|
To: | Patrick Dung <patrick_dkt(at)yahoo(dot)com(dot)hk>, Pgsql-general General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Use of 'now' constant datatype in view to take advantage of partitioned table |
Date: | 2014-08-21 07:59:42 |
Message-ID: | 1408607982.52086.YahooMailNeo@web193505.mail.sg3.yahoo.com |
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Thread: | |
Lists: | pgsql-general |
An update, inspired by Date LastDay - PostgreSQL wiki
Date LastDay - PostgreSQL wiki
Snippets Date LastDay() Works with PostgreSQL Any version Written in SQL Depends on Nothing by Scott Bailey 'Artacus'
View on wiki.postgresql.org Preview by Yahoo
1. Create a function like:
CREATE OR REPLACE FUNCTION now_function_ts_notz()
RETURNS timestamp without time zone AS
$BODY$
SELECT (NOW())::timestamp without time zone;
$BODY$
LANGUAGE sql IMMUTABLE STRICT
COST 100;
2. Create my View like this:
CREATE OR REPLACE VIEW v_recent_items AS
SELECT *
FROM food
WHERE food.post_timestamp >= (now_function_ts_notz() - '1 mon'::interval)::timestamp without time zone AND food.post_timestamp <= now()::timestamp without time zone
ORDER BY food.post_timestamp DESC
LIMIT 30;
While running 'EXPLAIN ANALYZE select * from v_recent_items'
I found that it skipped the partition table food_2013p.
Is it a valid work around? Or there is other better or elegant way?
Thanks and regards,
Patrick
On Thursday, August 21, 2014 3:21 PM, Patrick Dung <patrick_dkt(at)yahoo(dot)com(dot)hk> wrote:
Resent. As I could not see my mail in the mailing list after about two hours.
On Thursday, August 21, 2014 1:43 PM, Patrick Dung <patrick_dkt(at)yahoo(dot)com(dot)hk> wrote:
Hi Postgresql users,
I have a master table with two partition table (food_2013p, food_2014p).
I found that when I use SELECT + 'now' constant, constraint exclusion works, (it skipped the 2013 partition).
EXPLAIN ANALYZE
SELECT *
FROM food
WHERE food.post_timestamp >= ('now'::date - interval '1 month')::date AND food.post_timestamp <= 'now'
ORDER BY food.post_timestamp DESC
LIMIT 30;
But when I put the query inside view, 'now' is converted to the timestamp when I run the create view.
So the view becomes:
WHERE food.post_timestamp >= ('2014-08-21'::date - '1 mon'::interval)::date AND food.post_timestamp <= '2014-08-21 13:38:29.642347'::timestamp without time zone
This is not dynamic.
When I use now(), the query will scan other partition tables. I know this is a restriction of partition on non-immutable function.
Would it be possible or a feature request to take advantage of the partition table with query like this?
Thanks and regards,
Patrick
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