Re: bitmap index not used

I'd recommend you to take a dump.
A 10053 dump.
And see from there.

:)

Tanel.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, October 29, 2003 10:09 PM

> Hi,
>
> I have a puzzle.
>
> A bitmap index on a varchar2(25) column. table has 7131413 rows, of which
> 7125290 are null for the column in question, the rest of the rows are
unique
> values. There is a histogram on this column, it has 2 buckets.
>
> A select statement using this column in the where clause generates two
> plans, one which uses the index and one which doesn't. The deciding factor
> is the length of the string in the filter.
>
> select * from table where microchip_number = 'avid1'
> this produces a plan which uses the bitmap
>
> select * from table where microchip_number = 'avid12' (and any additional
> characters in the string )
> this produces a plan which uses a full table scan.
>
> I am stumped about how to figure out why the optimizer makes a choice
based
> upon the length of the string in the predicate.
>
> Much obliged,
>
> Josh
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Josh Collier
> INET: Josh.Collier_at_Banfield.net
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Tanel Poder
  INET: tanel.poder.003_at_mail.ee

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