Date: Sun, 05 Jun 2011 21:06:25 +0900
From: Masaru Sugawara <pgsql@amail.plala.or.jp>
To: pgsql-sql@postgresql.org
Subject: Re: selecting records X minutes apart
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References: <20110603195253.GE1324@slacker.ja10629.home>
Message-Id: <20110605210624.952F.2D56284C@amail.plala.or.jp>
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On Fri, 3 Jun 2011 15:52:53 -0400
lists-pgsql@useunix.net wrote:


I also think you might want to use WITH RECURSIVE clause. 
This SQL searches the case of an interval of 5 minutes or more, 
and sets a relationship between a parent to its child.


CREATE TABLE tbl(id integer, ts time) ;
INSERT INTO tbl VALUES
(0, '20:00'),
(0, '20:05'),
(0, '20:08'),
(0, '20:10'),
(0, '20:11'),   -- added as a sample. 
(1, '20:03'),
(1, '20:04'),
(1, '20:05'),
(1, '20:09'),
(1, '20:16');   -- added as a sample. 

SELECT * FROM tbl;


--
WITH RECURSIVE rec(id , ts_p, ts_c) AS (
SELECT a1.id, min(a1.ts), min(b1.ts)
   FROM tbl AS a1, tbl AS b1 
   WHERE a1.id=b1.id AND a1.ts + interval'5 minute' <= b1.ts 
   GROUP BY a1.id
UNION ALL
SELECT t2.id, t2.ts_p, t2.ts_c
   FROM rec AS t1 INNER JOIN 
   (SELECT a2.id, a2.ts as ts_p, min(b2.ts) AS ts_c
       FROM tbl AS a2, tbl AS b2 
       WHERE a2.id = b2.id AND a2.ts + interval'5 minute' <= b2.ts 
       GROUP BY a2.id, a2.ts
    UNION ALL
    SELECT a3.id, a3.ts, null
       FROM tbl AS a3      
    ) AS t2 ON t1.id = t2.id AND t1.ts_c=t2.ts_p
)
SELECT DISTINCT id, ts_p AS ts FROM rec
ORDER BY 1,2;


Regards,
Masaru Sugawara


> I have a table that, at a minimum, has ID and timestamp columns.  Records
> are inserted into with random IDs and timestamps.  Duplicate IDs are allowed. 
> 
> I want to select records grouped by ID, ordered by timestamp that are X minutes
> apart. In this case X is 5.
> 
> Note, the intervals are not X minute wall clock intervals, they are X minute
> intervals from the last accepted record, per-id.
> 
> For instance here is some sample input data:
> 
> ID	TS (HH:MM)
> -------------------
> 0	20:00
> 1	20:03
> 1	20:04
> 0	20:05
> 1	20:05
> 0	20:08
> 1	20:09
> 0	20:10
> 
> I'd want the select to return:
> 
> ID	TS (HH:MM)
> -------------------
> 0	20:00
> 0	20:05
> 0	20:10
> 1	20:03
> 1	20:09
> 
> 
> Does my question make sense?
> 
> Thanks in advance,
> Wayne
> 
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