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
FROM t2 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(at)postgresql(dot)org [mailto:pgsql-sql-owner(at)postgresql(dot)org]
On Behalf Of Michele Petrazzo - Unipex
Sent: Wednesday, May 26, 2010 7:35 PM
To: pgsql-sql(at)postgresql(dot)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