From: Jim C. Nasby <jnasby@pervasive.com>
To: Andreas Joseph Krogh <andreak@officenet.no>
Cc: pgsql-sql@postgresql.org
Subject: Re: Problem with query on history table
Date: Wed, 1 Mar 2006 16:19:43 -0600
Message-ID: <20060301221943.GX82012@pervasive.com> (raw)
In-Reply-To: <200602270819.30702.andreak@officenet.no>
References: <200602270819.30702.andreak@officenet.no>
Probably the easiest way is to switch to using table partitioning and
switch to using start_timestamp and end_timestamp, so that when you
modify a row you update the old one setting end_timestamp to now() and
insert the new row (all within one transaction).
There are other ways to do it, but they'll probably be much slower. I
don't think they require a lot of CASE statements though.
Show us what you were planning on doing and maybe I'll have more ideas.
On Mon, Feb 27, 2006 at 08:19:30AM +0100, Andreas Joseph Krogh wrote:
> Hi all!
>
> I don't know if there's a standard solution to the kind of problem I'm trying
> to solve, but I will appreciate your thougts(and maybe solution:) on this
> problem of mine:
>
> I have 2 tables: hist and curr which hold numbers for "history-data" and
> "current-data" respectivly. Here is a simplified version of the schema:
>
> CREATE TABLE curr (
> id integer NOT NULL,
> etc integer NOT NULL,
> created timestamp without time zone NOT NULL,
> modified timestamp without time zone
> );
>
> CREATE TABLE hist (
> id serial NOT NULL,
> curr_id integer NOT NULL REFERENCES curr(id),
> etc integer NOT NULL,
> modified timestamp without time zone NOT NULL
> );
>
> andreak=# SELECT * from curr;
> id | etc | created | modified
> ----+-----+---------------------+---------------------
> 1 | 5 | 2006-02-01 00:00:00 |
> 2 | 10 | 2006-01-15 00:00:00 | 2006-01-26 00:00:00
> 3 | 10 | 2006-01-08 00:00:00 | 2006-01-25 00:00:00
> (3 rows)
>
> andreak=# SELECT * from hist;
> id | curr_id | etc | modified
> ----+--------+-----+---------------------
> 1 | 3 | 30 | 2006-01-16 00:00:00
> 2 | 3 | 20 | 2006-01-25 00:00:00
> 3 | 2 | 20 | 2006-01-26 00:00:00
> (3 rows)
>
> Now - I would like to get a report on what the "ETC" is on a given entry in
> "curr" in a given "point in time". Let me explain. If I want status for 17.
> jan.(17.01.2006) I would like to get these numbers out from the query:
>
> id | created | curr_modified | hist_modified | etc
> ----+---------------------+---------------------+---------------------+-----
> 3 | 2006-01-08 00:00:00 | 2006-01-25 00:00:00 | 2006-01-16 00:00:00 | 30
> 2 | 2006-01-15 00:00:00 | 2006-01-26 00:00:00 | 2006-01-26 00:00:00 | 20
> 1 | 2006-02-01 00:00:00 | | | 5
>
>
> That is; If the entry is modified after it's created, a snapshot of the "old
> version" is copied to table "hist" with the hist.modified field set to the
> "modified-timestamp". So there will exist several entries in "hist" for each
> time an entry in "curr" is modified.
>
> If I want status for the 27. jan. I would like the query to return the
> following rows:
>
> id | created | curr_modified | hist_modified | etc
> ----+---------------------+---------------------+---------------------+-----
> 3 | 2006-01-08 00:00:00 | 2006-01-25 00:00:00 | 2006-01-25 00:00:00 | 10
> 2 | 2006-01-15 00:00:00 | 2006-01-26 00:00:00 | 2006-01-26 00:00:00 | 10
> 1 | 2006-02-01 00:00:00 | | | 5
>
> select curr.id, curr.created, curr.modified as curr_modified, hist.modified as
> hist_modified, coalesce(hist.etc, curr.etc) as etc FROM curr LEFT OUTER JOIN
> hist ON(curr.id = hist.curr_id) WHERE ...
>
> I'm really stuck here. It seems to me that I need a lot of
> CASE...WHEN...ELSE.. statements in the query, but is there an easier way?
>
> --
> Andreas Joseph Krogh <andreak@officenet.no>
>
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>
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-sql@postgresql.org
Cc: jnasby@pervasive.com, andreak@officenet.no
Subject: Re: Problem with query on history table
In-Reply-To: <20060301221943.GX82012@pervasive.com>
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