Re: rownum

> Y si quiero que un query arroje a lo mucho solo 3 registros como se deberia
> hacer? (en ORACLE "where rownum<=3")
>

The LIMIT and OFFSET clauses of SELECT allow the user to specify which
rows to return. For example, suppose customer has 1,000 rows with
customer_id values ranging from 1 to 1,000. Figure [*] shows queries
using LIMIT and LIMIT...OFFSET.

test=> SELECT customer_id FROM customer ORDER BY customer_id LIMIT 3;
customer_id
-------------
1
2
3
(3 rows)

test=> SELECT customer_id FROM customer ORDER BY customer_id LIMIT 3 OFFSET 997;
customer_id
-------------
998
999
1000
(3 rows)

The first query sorts the table by customer_id and uses LIMIT to return
the first three rows. The second query is similar, except that it skips
to the 997th row before returning three rows.

* * *
Podemos ver más información en
http://www.postgresql.org/docs/8.1/interactive/queries-limit.html
http://www.postgresql.org/files/documentation/books/aw_pgsql/node115.html

P.D. Roberto, tu último mensaje tienen fecha de octubre, es posible que
no te contesten en esta lista por los problemas que ello causa.