Re: inner join and limit - Mailing list pgsql-sql

I found a good solution.

drop table if exists t3;
drop table if exists t2;
drop table if exists t1;
create table t1 ( id int primary key, title varchar(10) );
insert into t1 values (1,'abcde'),(2,'fghi');
create table t2 (id int primary key,t1id int not null references t1 (id) ,somedate date);
insert into t2 values
(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');
create table t3 ( t1id int not null,idcount int,vector varchar[][] );
insert into t3 (t1id,idcount) select t1id,count(1) as idcount from t2 group by t1id;
update t3 set vector=array(select somedate from t2 where t2.t1id=t3.t1id ORDER BY somedate DESC LIMIT 2);
select * from t1;
select * from t2;
select * from t3;

I got this output...

rolando=# select * from t1;id | title
----+------- 1 | abcde 2 | fghi
(2 rows)

rolando=# select * from t2;id | t1id |  somedate
----+------+------------ 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 
(5 rows)

rolando=# select * from t3;t1id | idcount |         vector
------+---------+------------------------   2 |       2 | {2010-05-26,2010-05-22}   1 |       3 |
{2010-05-25,2010-05-24}


Notice the arrays are length 2 because I have the clause "LIMIT 2" in the UPDATE command.
You can set LIMIT to whatever. Give it a try !!!

BTW I think another person already replied a solution without an extra table. Give that a try, too !!!

-----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 1:35 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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