Re: inner join and limit

I can only see a LIMIT 1 possible. If someone can come up with LIMIT N on this one, please let us all know.

rolando=# drop table if exists t2;
DROP TABLE
rolando=# drop table if exists t1;
DROP TABLE
rolando=# create table t1 ( id int primary key, title varchar(10) );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t1_pkey" for table "t1"
CREATE TABLE
rolando=# insert into t1 values (1,'abcde'),(2,'fghi');
INSERT 0 2
rolando=# create table t2 (id int primary key,t1id int not null references t1 (id) ,somedate date);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t2_pkey" for table "t2"
CREATE TABLE
rolando=# insert into t2 values
rolando-# (1,1,'2010-05-23'),
rolando-# (2,1,'2010-05-24'),
rolando-# (3,1,'2010-05-25'),
rolando-# (4,2,'2010-05-22'),
rolando-# (5,2,'2010-05-26');
INSERT 0 5
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 t1.id,t2.id,t2.somedate
rolando-# from t1,t2,(select t1id,max(somedate) as somedate from t2 group by t1id) t3
rolando-# where t1.id=t2.t1id
rolando-# and t2.somedate=t3.somedate;id | id |  somedate
----+----+------------ 1 |  3 | 2010-05-25 2 |  5 | 2010-05-26
(2 rows)


Rolando A. Edwards
MySQL DBA (CMDBA)

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-----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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