Re: Optimization of query finding related products for a certain product
Date: Tue, 11 Sep 2001 01:26:04 -0700
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) =================================================================== * Check out Database Debunkings (http://www.firstsql.com/dbdebunk/) * "Where Persistent Prevailing Database Fallacies Are Dispelled"Received on Tue Sep 11 2001 - 10:26:04 CEST