RE: [HACKERS] Idea for speeding up uncorrelated subqueries
От | Ansley, Michael |
---|---|
Тема | RE: [HACKERS] Idea for speeding up uncorrelated subqueries |
Дата | |
Msg-id | 1BF7C7482189D211B03F00805F8527F70ED0C3@S-NATH-EXCH2 обсуждение исходный текст |
Список | pgsql-hackers |
I thought that all correlated and uncorrelated sub-queries could be rewritten as a join, simplifying the query tree. It should be a mechanical process which can probably be performed in the rewriter. Somebody put me right. MikeA >> -----Original Message----- >> From: Bruce Momjian [mailto:maillist@candle.pha.pa.us] >> Sent: Friday, August 06, 1999 7:11 AM >> To: Tom Lane >> Cc: Vadim Mikheev; pgsql-hackers@postgreSQL.org >> Subject: Re: [HACKERS] Idea for speeding up uncorrelated subqueries >> >> >> > Bruce Momjian <maillist@candle.pha.pa.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? >> >> Yes, we have the nice subselect feature. I just hate to see it not >> completely finished, performance-wise. >> >> -- >> Bruce Momjian | http://www.op.net/~candle >> maillist@candle.pha.pa.us | (610) 853-3000 >> + If your life is a hard drive, | 830 Blythe Avenue >> + Christ can be your backup. | Drexel Hill, >> Pennsylvania 19026 >>
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