From: Richard Broersma Jr <rabroersma@yahoo.com>
To: Henry Ortega <juandelacruz@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Re: Fastest way to get max tstamp
Date: Mon, 28 Aug 2006 12:23:07 -0700 (PDT)
Message-ID: <20060828192307.54202.qmail@web31815.mail.mud.yahoo.com> (raw)
In-Reply-To: <2bffcc330608281110j404e3fd1q9d6d27a6a97ad31d@mail.gmail.com>
> name | program | effective | tstamp | rate
> ------+---------+------------+----------------------------+------
> jdoe | AAA | 2006-07-01 | 2006-07-16 23:42:13.809214 | 20
> jdoe | BBB | 2006-07-01 | 2006-07-16 23:42:13.809214 | 20
> jdoe | AAA | 2006-08-16 | 2006-08-25 11:56:50.380575 | 20
> jdoe | BBB | 2006-08-16 | 2006-08-25 11:56:50.380575 | 20
> jdoe | AAA | 2006-08-16 | 2006-08-25 11:57:17.394854 | 20
> jdoe | BBB | 2006-08-16 | 2006-08-25 11:57:17.394854 | 20
> jdoe | AAA | 2006-09-01 | 2006-08-28 12:38:42.486513 | 20
> jdoe | BBB | 2006-09-01 | 2006-08-28 12:38:42.486513 | 20
>
> I want to get:
> name | program | effective | tstamp | rate
> ------+---------+------------+----------------------------+------
> jdoe | AAA | 2006-07-01 | 2006-07-16 23:42:13.809214 | 20
> jdoe | BBB | 2006-07-01 | 2006-07-16 23:42:13.809214 | 20
> jdoe | AAA | 2006-08-16 | 2006-08-25 11:57:17.394854 | 20
> jdoe | BBB | 2006-08-16 | 2006-08-25 11:57:17.394854 | 20
> jdoe | AAA | 2006-09-01 | 2006-08-28 12:38:42.486513 | 20
> jdoe | BBB | 2006-09-01 | 2006-08-28 12:38:42.486513 | 20
>
> Basically, for effective='08-16-2006', it only gets the latest inserted
> record (using tstamp) for that effective date, which is 2006-08-25 11:57:
> 17.394854.
>
> So what is the quickest way to do this?
> I can always do:
> Select * from Table t where tstamp=(select max(tstamp) from Table t2 where
> t2.name=t.name and t2.effective=t.effective)
> but it takes so long since this is a huge table.
>
> Any suggestions?
SELECT name, program, effective, tstamp, rate
FROM TABLE AS T1
JOIN
(
SELECT max(tstamp) as maxtstamp
FROM Table
WHERE tstamp between current_timestamp - interval '7 days' and current_timestamp
GROUP BY name, program, effective
) AS T2
ON (T1.tstamp = T2.maxtstamp)
;
A smaller date range on a large table will really speed up your query also. If you really need to
see the results of the same table over and over again, a materialized view(i.e. push the query
results into a table and then add incremental updates over time) would probably work better for you.
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To: pgsql-sql@postgresql.org
Cc: rabroersma@yahoo.com, juandelacruz@gmail.com
Subject: Re: Fastest way to get max tstamp
In-Reply-To: <20060828192307.54202.qmail@web31815.mail.mud.yahoo.com>
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