Re: Individual Indexes v.s. One "combinded" Index
Date: Tue, 11 Oct 94 21:34:00 -0300
Message-ID: <2aa.426.846%mpcbbs_at_ibase.org.br>
On 12 Oct 94 12:35am, wrote to ALL:
> Newsgroup: comp.databases.oracle
> Organization: Health, Housing, Local Government and Community Services
> In article <2aa.456.846%mpcbbs_at_ibase.org.br>, Carlos.Netto_at_ibase.org.br
> (Carlos Netto) writes: >
> ...stuff deleted ...
>> >> a) search for value 1 -> 10,000 rows scan (in avarange, of course) >> b) search for value 6 -> 10,000 rows scan (in avarange, of course) >> c) search for value 3 -> 10,000 rows scan (in avarange, of course) >> d) search for value 9 -> 10,000 rows scan (in avarange, of course) >> e) search for value 2 -> 10,000 rows scan (in avarange, of course) >> f) search for value 0 -> 10,000 rows scan (in avarange, of course)
> I may have miss-understood what you were trying to say but ...
> Oracle will pick ONE index and retrieve all rows that satisfy THAT single
> criteria AND then examine each identified row to exclude those that fail
> the other column criteria.
I wrote that Oracle can do something different, but ever less
efficient than a concatenated index.
> This is the reason why it is best to have a concatenated index (or as
> unique as possible) that narrows down the candidate search rows very
> quickly.
Of course. Sorry if you wrote it and I didn't understand it.
[deleted lines]
> I have never seen Oracle do the multiple index scanning (on one table) and
> then sort-merge that you have detailed above.
I have seen it onece, but only for two index (not six). The operation
described on explain isn't "sort-merge", but "and-equal".
bye,
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Received on Wed Oct 12 1994 - 01:34:00 CET