Re: Help with a JOIN.

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

<rest snipped>

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;

is

ticket_id | ticket_description | c_max_date | comments_comment
-----------+--------------------+------------+-----------------------
3 | ticket 3 | 1089386130 | comment 3 on ticket 4 <<===
matches a timestamp for ticket 4
3 | ticket 3 | 1089386130 | comment 4 on ticket 3
4 | ticket 4 | 1151680530 | comment 4 on ticket 4

The result I want is

ticket_id | ticket_description | c_max_date | comments_comment
-----------+--------------------+------------+-----------------------
3 | ticket 3 | 1089386130 | comment 4 on ticket 3
4 | ticket 4 | 1151680530 | comment 4 on ticket 4

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(at)tcd(dot)ie

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