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Home -> Community -> Usenet -> c.d.o.server -> Re: Optimization of UNION
Was it 7.3.4 perhaps - there a a few things that are in 7.3.4 and 8.1 but not in 8.0.
This optimizer trick is a new one on me though. I knew that an IN list could be converted to a UNION ALL, but I didn't think it could work the other way round, and when I read the post I thought it VERY unlikely that a UNION would be converted.
--
Jonathan Lewis
Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
Connor McDonald wrote in message <37D7A19B.496D_at_yahoo.com>...
>
>Interesting, I was giving a tuning course the other day, and this
>intersting thing came up
>
>In 7.3
>
>select ...
>from table
>where un_indexed_col = val1
>UNION ALL
>select ...
>from table
>where un_indexed_col = val1
>
>was (correctly) changed to OR and thus one scan by the optimiser...The
>same thing in 8.0.5 (same schema, blocksize, tables etc) did not...Hmmm
>
Received on Thu Sep 09 1999 - 14:15:44 CDT