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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Problem with understanding Optimization methods.
Hi Jonathan,
What release did this NULL_CHECK start with?
I used to see:
Execution Plan
As I recall, I used-to need an FBI on column with NULL values
create index
i1
on
t1
(nvl(n1,'null'))
;
Regards,
Donald K. Burleson
www.dba-oracle.com
www.remote-dba.net
>
> Conversely, the CBO is a lot smarter with
> this scenario that people realise. How many
> people knew that Oracle can resolve a query
> of the type:
> where colX is null
> using a b-tree index ?
>
> Try this --
>
> drop table t1;
>
> create table t1 (n1 number, n2 number not null, n3 number);
> create index i1 on t1 (n1, n2);
>
> set autotrace traceonly explain
> select /*+ first_rows */ * from t1 where n1 is null;
> set autotrace off
>
> Execution Plan
> ----------------------------------------------------------
> 0 SELECT STATEMENT Optimizer=HINT: FIRST_ROWS (Cost=4 Card=4
> Bytes=156)
> 1 0 TABLE ACCESS (BY INDEX ROWID) OF 'T1' (TABLE) (Cost=4 Card=4
> Bytes=156)
> 2 1 INDEX (RANGE SCAN) OF 'I1' (INDEX) (Cost=4 Card=4)
>
>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> The educated person is not the person
> who can answer the questions, but the
> person who can question the answers -- T. Schick Jr
>
>
> Next public appearance2:
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>
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Thursday, January 08, 2004 11:54 AM
>
>
> Bambi,
>
> Yes it is expected behaviour, but only when it is guaranteed that no rows
> will be missed because of unindexed null entries.
> I wanted to point out that RBO is too "dumb" to realize that even though
it
> ordered by column A which could be null, the column B in composite index
was
> not null, thus causing every row to be indexed and RBO didn't use the
index.
>
> Tanel.
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Jonathan Lewis
> INET: jonathan_at_jlcomp.demon.co.uk
>
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Don Burleson INET: don_at_burleson.cc Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Thu Jan 08 2004 - 07:59:25 CST
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