Re: inner join and limit

Hello
Here a suggestion for your problem.

SELECT a.id AS t1_id, d.id AS t2_id, d.somedate AS t2_somedate
FROM t1 a
JOIN  (   SELECT id, t1id, somedate   FROM t2 b   WHERE (t1id, somedate) IN      (       SELECT t1id, somedate
FROMt2 c       WHERE c.t1id = b.t1id       ORDER BY somedate DESC       LIMIT 1     ) ) d 
 
ON (a.id=d.t1id);

t1_id | t2_id | t2_somedate
-------+-------+-------------    1 |     3 | 2010-05-25    2 |     5 | 2010-05-26
(2 rows)


Hope this helps

Regards (Saluti da Zurigo)
Luigi Antognini



-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of Michele Petrazzo - Unipex
Sent: Wednesday, May 26, 2010 7:35 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] inner join and limit

Hi list,
I have two table that are so represented:
t1:
id int primary key
... other

t2:
id int primary key
t1id int fk(t1.id)
somedate date
... other

data t1:
1 | abcde
2 | fghi

data t2:
1 | 1 | 2010-05-23
2 | 1 | 2010-05-24
3 | 1 | 2010-05-25
4 | 2 | 2010-05-22
5 | 2 | 2010-05-26

I'm trying to create a query where the data replied are:
join t1 with t2 and return only the LIMIT 1 (or N) of the t2, with date 
order (of t2).
Data should be:

t1.id | t2.id | t2,somedate
1 | 3 | 2010-05-25
2 | 5 | 2010-05-26


As said, I'm trying, but without success...
Can be done for you?

Thanks,
Michele

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