Re: [HACKERS] Idea for speeding up uncorrelated subqueries

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: Vadim Mikheev <vadim(at)krs(dot)ru>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Idea for speeding up uncorrelated subqueries
Date: 1999-08-06 04:14:50
Message-ID: 6783.933912890@sss.pgh.pa.us
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Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> Isn't it something that takes only a few hours to implement. We can't
> keep telling people to us EXISTS, especially because most SQL people
> think correlated queries are slower that non-correlated ones. Can we
> just on-the-fly rewrite the query to use exists?

I was just about to suggest exactly that. The "IN (subselect)"
notation seems to be a lot more intuitive --- at least, people
keep coming up with it --- so why not rewrite it to the EXISTS
form, if we can handle that more efficiently?

regards, tom lane

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