Thank you very much for the explanation,
regards, Wolf
Sybrand Bakker <postmaster_at_sybrandb.demon.nl> schrieb in im Newsbeitrag:
938896894.15171.0.pluto.d4ee154e_at_news.demon.nl...
> Hi Wolf,
> There is a practical and theoretical approach to this.
> 1 practical
> If you are using the Rule Based Optimizer, Oracle will use the index, it
> will perform a range scan, and your data will be ordered.
> If you are using the Cost Based Optimizer, the optimizer will most likely
> decide you are retrieving all records and not use the index.
> In this case the data will return unsorted, and you need to do an order
by.
> It is very likely you will be better off NOT using the index, and using a
> full table scan followed by sort-merge, as this will use
> db_file_multiblock_count and return 8 or 16 blocks in one I/O.
> 2 theoretical.
> Officially you should not rely on any implicit order of the data. Also, as
> SQL is a relational language, and any set is by design unordered, this
> shouldn't be an issue.
>
> Bottom line: if ordering is really important, you shouldn't rely on the
use
> of indexes, especially not when using cost based optimizer.
> In group by you should definitely NOT rely on any implicit ordering.
>
> Hth,
>
>
> --
> Sybrand Bakker, Oracle DBA
> Wolf Grossi <wg_at_REMOVE_ANTI_SPAMmagro-soft.com> wrote in message
> news:37f623cb.0_at_195.70.96.56...
> > Hi folks,
> > can anyone tell me if it is granted that the results of the below
> > select, assuming that c01 is an ascending index, are in ascening order:
> > SELECT * FROM TAB01 WHERE C01 >= ' ';
> > Is there any hint in the ORACLE Docu (7 or 8); I could not find any
hint.
> > Thanks, Wolf
> >
> >
> >
> >
> >
>
>
Received on Sun Oct 03 1999 - 05:28:05 CDT
