On Thursday 04 December 2008 15:09, Gregory Stark wrote: > tmp <[EMAIL PROTECTED]> writes:
> > Also, it is my impression that many people use LIMIT to minimize the > > evaluation time of sub queries from which the outer query only needs a > > small subset of the sub query output. > > I've seen lots of queries which only pull a subset of the results too -- > but it's always a specific subset. So that means using ORDER BY or a WHERE > clause to control it. I use "ORDER BY random() LIMIT :some_small_number" frequently to get a "feel" for data. That always builds the unrandomized relation and then sorts it. I guess an alternate path for single-table queries would be to randomly choose a block number and then a tuple number; but that would be biased toward long rows (of which fewer can appear in a block). -- David Lee Lambert ... Software Developer Cell phone: +1 586-873-8813 ; alt. email <[EMAIL PROTECTED]> or <[EMAIL PROTECTED]> GPG key at http://www.lmert.com/keyring.txt -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
