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Turn correlated in subquery into join 2+ messages / 2 participants [nested] [flat]
* Turn correlated in subquery into join @ 2008-03-24 07:21 Dennis Bjorklund <db@zigo.dhs.org> 0 siblings, 1 reply; 2+ messages in thread From: Dennis Bjorklund @ 2008-03-24 07:21 UTC (permalink / raw) To: pgsql-performance Look like the mysql people found a subquery that postgresql doesn't handle as good as possible: http://s.petrunia.net/blog/ Is there some deeper issue here that I fail to see or is it simply that it hasn't been implemented but is fairly straigt forward? In the link above they do state that it isn't a very common case anyway. /Dennis ^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Turn correlated in subquery into join @ 2008-03-24 16:30 Tom Lane <tgl@sss.pgh.pa.us> parent: Dennis Bjorklund <db@zigo.dhs.org> 0 siblings, 0 replies; 2+ messages in thread From: Tom Lane @ 2008-03-24 16:30 UTC (permalink / raw) To: Dennis Bjorklund <db@zigo.dhs.org>; +Cc: pgsql-performance Dennis Bjorklund <db@zigo.dhs.org> writes: > Look like the mysql people found a subquery that postgresql doesn't > handle as good as possible: > http://s.petrunia.net/blog/ > Is there some deeper issue here that I fail to see or is it simply that > it hasn't been implemented but is fairly straigt forward? I don't think it's straightforward: you'd need to do some careful analysis to prove under what conditions such a transformation would be safe. If the answer is "always, it doesn't matter what the correlation condition is" then the actual implementation would probably not be tremendously difficult. If there are restrictions then checking whether the restrictions hold could be interesting ... regards, tom lane ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2008-03-24 16:30 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2008-03-24 07:21 Turn correlated in subquery into join Dennis Bjorklund <db@zigo.dhs.org> 2008-03-24 16:30 ` Tom Lane <tgl@sss.pgh.pa.us>
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