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Re: Help with a JOIN. - Mailing list pgsql-novice

From	Paul Linehan
Subject	Re: Help with a JOIN.
Date	July 21, 2014 01:25:46
Msg-id	CAF4RT5SG2d9wMKjYhzchwdKhZ_9rCSbcu6sk_9LpSTG6JJsEMw@mail.gmail.com Whole thread Raw
In response to	Re: Help with a JOIN. (Ken Benson <Ken@infowerks.com>)
Responses	Re: Help with a JOIN. (Paul Linehan <linehanp@tcd.ie>) Re: Help with a JOIN. (David G Johnston <david.g.johnston@gmail.com>)
List	pgsql-novice

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[[KenB]] You're asking for the MAX(comments_comment) …

Thanks for that Ken - just another small question for the list though.

Your query works perfectly for the data that I posted, however, I have data which has
duplicated dates (see DDL and DML below).

With this data, the result of your query

SELECT t.ticket_id, t.ticket_description, x.c_max_date, z.comments_comment
FROM
(
   SELECT ticket_id, MAX(c.comments_timestamp) AS c_max_date
   FROM comment c
   WHERE c.comments_timestamp < extract(epoch FROM TIMESTAMP '2014-07-20') - 60000000
   GROUP BY ticket_id
)
AS x INNER JOIN ticket AS t ON t.ticket_id = x.ticket_id
INNER JOIN comment AS z ON z.comments_timestamp = x.c_max_date;

The result I want is

Running this query on the comments table
select ticket_id, comment_id, comments_timestamp
from comment where ticket_id IN (3, 4)
order by ticket_id, comment_id, comments_timestamp;

gives

ticket_id | comment_id | comments_timestamp
-----------+------------+--------------------
         3 |          9 |         1007133330
         3 |         10 |         1013613330
         3 |         11 |         1088608530

3 | 12 | 1089386130 <<-- matches on ticket 4

4 | 13 | 1070205330
4 | 14 | 1076685330

4 | 15 | 1089386130 <<-- matches on ticket 3

4 | 16 | 1151680530

The problem is that the last date for ticket 3 matches a date (not the last)
for ticket 4.

Is there any way that I can pick up only the latest ticket in this case - you may
assume that comment_id is some sort of auto incrementing field - but I can't include

comment_id in my x subquery. I've been experimenting, but to no avail.

TIA and rgs,

Paul...

======== DDL and DML for my problem ====================

CREATE TABLE IF NOT EXISTS ticket
(
ticket_id INT NOT NULL,
ticket_description VARCHAR(25),
PRIMARY KEY (ticket_id)
);

CREATE TABLE IF NOT EXISTS comment
(
comment_id INT NOT NULL,
ticket_id INT NOT NULL,
comments_comment VARCHAR(45) NULL,
comments_timestamp INT NULL,
PRIMARY KEY (comment_id)
);

INSERT INTO ticket VALUES(1, 'ticket 1');
INSERT INTO ticket VALUES(2, 'ticket 2');
INSERT INTO ticket VALUES(3, 'ticket 3');
INSERT INTO ticket VALUES(4, 'ticket 4');
INSERT INTO ticket VALUES(5, 'ticket 5');

INSERT INTO comment VALUES(1, 1, 'comment 1 on ticket 1', extract(epoch FROM TIMESTAMP '2013-11-30 15:15:30'));
INSERT INTO comment VALUES(2, 1, 'comment 2 on ticket 1', extract(epoch FROM TIMESTAMP '2014-02-13 15:15:30'));
INSERT INTO comment VALUES(3, 1, 'comment 3 on ticket 1', extract(epoch FROM TIMESTAMP '2014-06-30 15:15:30'));
INSERT INTO comment VALUES(4, 1, 'comment 4 on ticket 1', extract(epoch FROM TIMESTAMP '2014-07-09 15:15:30'));
INSERT INTO comment VALUES(5, 2, 'comment 1 on ticket 2', extract(epoch FROM TIMESTAMP '2013-11-30 15:15:30'));
INSERT INTO comment VALUES(6, 2, 'comment 2 on ticket 2', extract(epoch FROM TIMESTAMP '2014-02-13 15:15:30'));
INSERT INTO comment VALUES(7, 2, 'comment 3 on ticket 2', extract(epoch FROM TIMESTAMP '2014-07-30 15:15:30'));
INSERT INTO comment VALUES(8, 2, 'comment 4 on ticket 2', extract(epoch FROM TIMESTAMP '2014-08-09 15:15:30'));
INSERT INTO comment VALUES(9, 3, 'comment 1 on ticket 3', extract(epoch FROM TIMESTAMP '2001-11-30 15:15:30'));
INSERT INTO comment VALUES(10, 3, 'comment 2 on ticket 3', extract(epoch FROM TIMESTAMP '2002-02-13 15:15:30'));
INSERT INTO comment VALUES(11, 3, 'comment 3 on ticket 3', extract(epoch FROM TIMESTAMP '2004-06-30 15:15:30'));
INSERT INTO comment VALUES(12, 3, 'comment 4 on ticket 3', extract(epoch FROM TIMESTAMP '2004-07-09 15:15:30'));
INSERT INTO comment VALUES(13, 4, 'comment 1 on ticket 4', extract(epoch FROM TIMESTAMP '2003-11-30 15:15:30'));
INSERT INTO comment VALUES(14, 4, 'comment 2 on ticket 4', extract(epoch FROM TIMESTAMP '2004-02-13 15:15:30'));
INSERT INTO comment VALUES(15, 4, 'comment 3 on ticket 4', extract(epoch FROM TIMESTAMP '2004-07-09 15:15:30'));
INSERT INTO comment VALUES(16, 4, 'comment 4 on ticket 4', extract(epoch FROM TIMESTAMP '2006-06-30 15:15:30'));
INSERT INTO comment VALUES(17, 5, 'comment 1 on ticket 1', extract(epoch FROM TIMESTAMP '2013-11-30 15:15:30'));
INSERT INTO comment VALUES(18, 5, 'comment 2 on ticket 2', extract(epoch FROM TIMESTAMP '2014-02-13 15:15:30'));
INSERT INTO comment VALUES(19, 5, 'comment 3 on ticket 3', extract(epoch FROM TIMESTAMP '2014-06-30 15:15:30'));
INSERT INTO comment VALUES(20, 5, 'comment 4 on ticket 4', extract(epoch FROM TIMESTAMP '2014-07-09 15:15:30'));

--

linehanp@tcd.ie

Mob: 00 353 86 864 5772

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From: "ktm@rice.edu"
Date: 21 July 2014, 00:36:22
Subject: Re: Creating a hot copy of PostgreSQL database

From: Albe Laurenz
Date: 21 July 2014, 10:38:35
Subject: Re: Creating a hot copy of PostgreSQL database

Re: Help with a JOIN. - Mailing list pgsql-novice

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