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Re: Optimization of query finding related products for a certain product

From: Lee Fesperman <firstsql_at_ix.netcom.com>
Date: Tue, 11 Sep 2001 01:26:04 -0700
Message-ID: <3B9DCA9C.35D6@ix.netcom.com>


David Cressey wrote:
> With regard to EXISTS, I'm a little surprised. DEC Rdb always use to give
> me BETTER response with
> EXISTS, when appropriate, because the optimizer had a special "fast first"
> algorithm it could use in that case.

IN, =ANY, =ALL can also benefit from a "fast first" algorithm.

> My understanding was that the CBO put into Oracle V8 was heavily influenced
> by DEC Rdb's optimizer.
> Oracle bought DEC Rdb in 1994, and called it Oracle Rdb. I wonder what
> went wrong with EXISTS.
>
> I've never had such bad luck with EXISTS in Oracle, either. But I may not
> have put it to a severe enough test.

Technically, IN, =ANY, =ALL and EXISTS can all be transformed into each other, if you ignore the 'EXISTS error' in standard SQL.

-- 
Lee Fesperman, FFE Software, Inc. (http://www.firstsql.com)
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Received on Tue Sep 11 2001 - 03:26:04 CDT

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